Mining  efept. 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


NOTES  ON 

METALLURGICAL  MILL 
CONSTRUCTION 


EDITED    BY 

W.    R.    INGALLS. 

ti 


FIRST    EDITION 


OF  THE 

{    UNIVERSITY  ) 

OF 


1906 
THE    ENGINEERING    AND    MINING    JOURNAL 

505  PEARL  STREET,  NEW  YORK 
20  BUCKLERSBURY,    -     -    LONDON,  E.  C. 


14 


Copyright,  1906 
BY  THE  ENGINEERING  AND  MINING  JOURNAL. 

Also  Entered  at 

HTATJONKK8'  HALL,  LONDON,   ENGLAND. 

All  rights  reserved. 


PREFACE 

THIS  book  is  a  reprint  of  a  series  of  articles,  bearing  upon 
some  of  the  important  details  that  enter  into  the  construction  of 
metallurgical  plants,  especially  mills  of  various  kinds,  which 
have  appeared  in  the  Engineering  and  Mining  Journal,  chiefly 
during  the  last  three  years;  in  a  few  cases  articles  from  earlier 
issues  have  been  inserted,  in  view  of  their  special  importance; 
and  there  is  one  article  from  the  Pacific  Coast  Miner.  Some  of 
the  articles  are  abstracts  of  papers  originally  presented  before 
engineering  societies,  subsequently  published  in  the  Engineering 
and  Mining  Journal,  as  to  which  proper  acknowledgment  has 
been  made. 

The  articles  comprised  in  this  book  relate  to  a  variety  of 
subjects,  which  are  of  great  importance  in  the  design,  construc- 
tion, and  operation  of  metallurgical  mills,  but  have  not  been 
treated  with  any  fullness  in  technical  literature,  save  in  the 
periodical  literature  and  transactions  of  the  engineering  societies, 
wherein  they  escape  general  availability.  For  this  reason,  it 
has  appeared  useful  to  collect  and  republish  in  convenient  form 
the  articles  of  this  character  which  have  previously  been  printed 
in  the  Engineering  and  Joining  Journal. 

I  recognize  fully  the  deficiencies  of  the  present  work,  not 
referring,  however,  to  the  value  of  the  articles  herein  assembled, 
but  rather  to  their  heterogeneous  character,  and  the  absence  of 
contributions  on  many  important  subjects,  which  would  be 
necessary  to  round  out  a  general  treatise  on  metallurgical  mill 
construction.  I  hope,  therefore,  that  the  readers  of  the  book 
will  appreciate  my  intention,  and  will  accept  the  book  simply  as 
a  series  of  notes  and  essays,  covering  some  of  the  principal  subjects 
upon  which  the  engineers  of  four  continents  have  written  during 
the  last  three  years. 

W.  R.  INGALLS. 

JUNE  1,   1906. 

in 


184416 


TABLE  OF  CONTENTS 

PART  I 
BRICKWORK  AND  CONCRETE 

PAGE 

COST  OF  EARTH  WORK  (EDITORIAL) 3 

BRICK  MASONRY  (W.  R.  INGALLS) 5 

SAND-LIMB  BRICK  (EDITORIAL) 7 

CONCRETE  MIXTURE  (EDITORIAL) 8 

REQUIREMENTS  FOR  CONCRETE  (EDITORIAL)     ........  9 

LIMESTONE  SCREENINGS  FOR  USE  IN  CONCRETE  (EDITORIAL)       ...  10 

RUBBLE  CONCRETE  (EDITORIAL) li 

CONCRETE  WORK  ABOUT  MINES  (HENRY  W.  EDWARDS)  ......  13 

CONCRETE  FOUNDATIONS  AND  FLOORS  (EDITORIAL) 18 

PART  II 
BUILDING  CONSTRUCTION 

DESIGN  OF  MILL  BUILDINGS  (EDITORIAL) 23 

COST  OF  A  SINGLE-FLOOR  MILL  (EDITORIAL) 24 

LIGHTING  OF  WORKSHOPS  (EDITORIAL) 25 

LIGHTING  OF  MILL  BUILDINGS  (C.  A.  RAYMOND) 26 

HOLLOW  BRICK  FOR  MILL-BUILDING  CONSTRUCTION  (EDITORIAL)     .      .  28 

NEW  USES  OF  CONCRETE  IN  BUILDING  CONSTRUCTION  (EDITORIAL)         .  31 

CORRUGATED  IRON  BUILDINGS  (W.  R.  INGALLS)   .......  34 

IRON  AND  STEEL  BUILDINGS  (EDITORIAL) 38 

NOTES  ON  TIMBER  (EDITORIAL) 39 

DESIGN  OF  TIMBER  TRUSSES  (EDITORIAL) 40 

SAW-TOOTHED  ROOF  CONSTRUCTION  (EDITORIAL) 42 

NOTES  ON  ROOFS  AND  ROOF  COVERINGS  (W.  R.  INGALLS)       ....  45 

PROTECTION  OF  IRON  AND  STEEL  (EDITORIAL) 51 

PROTECTION  OF  STEEL  FROM  CORROSION  (CHARLES  L.  NORTON)   ...  54 

SPECIFICATIONS  FOR  PAINTING  STEEL  STRUCTURAL  WORK  (EDITORIAL)  55 

STAMP  MILL  CONSTRUCTION  (EDITORIAL) 57 

DESIGN  OF  ORE-BINS  AND  COAL-POCKETS  (EDITORIAL) 58 

NEW  CHANGING-HOUSE  AT  CLIFFS  SHAFT  MINE  (JOHN  S.  MENNIE)     .      .  59 

DUST-PROOF  PARTITIONS  (EDITORIAL) 64 

v 


Vi  TABLE  OF  CONTENTS 

PART   III 
ORE-CRUSHING  MACHINERY 

PAGE 

CAPACITY  OF  BLAKE  CRUSHERS  (W.  R.  INGALLS)   .......  67 

A  CANTILEVER  BATTERY  FRAME  (!RA  C.  Boss)  './,-•'   .      .      ...  70 

BATTERY  FOUNDATIONS  (H.  E.  WEST) 75 

BATTERY  FOUNDATIONS  (M.  P.  Boss)  ,    ' 77 

STAMP  TAPPETS  (M.  P..  Boss)     :      .     ,      .,,,,,-; 79 

HORSE-POWER  FOR  TEN-STAMP  BATTERY  (FRANK  E.  SHEPARD).     ,     .  82 

THE  DRY  CRUSHING  OF  ORE  (EDITORIAL)  .      .   :.     \  ""-.    ' '.   '  :'  ''••':"•    /  '  $4  ' 

MODERN  CRUSHING  AND  GRINDING  MACHINERY  (PHILIP  ARGALL)"   .    '""'.  109 

SPRINGS  ON  CRUSHING  ROLLS  (LEWIS  SEARING)   .      .'    .      .      '.     :    '  .  115 

NOTES  ON  SOME  REGRINDING  MACHINES  (MARTIN  SCHWERIN)   .      .:     .  118 

REGRINDING  MACHINERY  (S.  V.  TRENT)     .      ...      .      .      .      .  *'.''  127 

REGRINDING  MACHINERY  (GEORGE  E.  COLLINS)     .      .      .      .      .      .  :  .  130 

THE  FERRARIS  BALL-MILL  (W.  R.  INGALLS)     .      ...      .      .      .      .  132 ; 

THE  OPERATION  OF  A  TUBE-MILL  (HERMANN  FISCHER)   :      .      .      .      .  137 ' 

THE  THEORY  OF  THE  TUBE-MILL  (H.  A.  WHITE)   .      .      .      .      .      .     v  145 

TUBE-MILL  NOTES  (ALFRED  JAMES) 151 

TUBE-MILLS  (H.  W.  HARDINGE) 154 

CHILEAN  MILLS  (M.  P.  Boss)     .      .      .      .      .      . 156 

PART  IV 
DRIERS  AND  DRYING 

ORE  DRYING  (W.  R.  INGALLS) 161 

NOTES  ON  ORE  AND  COAL  DRYING  (C.  O.  BARTLETT) 165 

GRINDING  MACHINES  USED  AT  KALGOORLIE  (W.  E.  SIMPSON)   .      .      .  167 

PART  V 

CONVEYORS  AND  ELEVATORS 

MECHANICAL  CONVEYORS  (W.  R,  INGALLS)     ........  173 

BELT  ELEVATORS  (W.  R.  INGALLS) 185 

TAILINGS  ELEVATORS  (W.  H.  WOOD  AND  E.  J.  LASCHINGER),  ....  190 

TAILINGS  ELEVATORS  (R.  GILMAN  BROWN) 198 

PART  VI 

DISPOSAL  OF  TAILINGS 
A  SYSTEM  OF  HANDLING  SAND  MECHANICALLY  FOR  CYANIDE  VATS 

(CHARLES  BUTTERS  AND  ALBERT  F.  CRANK)   .      .      ..     .      .     .     .  203 


TABLE  OF  CONTENTS  vii 

PAGE 

ECONOMY  IN  MILL  WATER  (JESSE  C.  SCOBEY) 214 

REMOVAL  OF  SAND  FROM  WASTE  WATER  (J.  E.  JOHNSON,  JR.)   .      .     .  224 

DISPOSITION  OF  TAILINGS  (EDITORIAL) 228 

PART  VII 

MISCELLANEOUS 

RUBBERS  AND  RUBBER  BELTING  (EDITORIAL) 233 

COAL-DUST  FIRING  (C.  O.  BARTLETT) 236 

INTERNALLY  FIRED  BOILERS  (EDITORIAL) 238 

ACCIDENTS  TO  MOTORS  AND  DYNAMOS  (A.  C.  CORMACK) 240 

ALLOYS  FOR  BEARING  PURPOSES  (G.  H.  CLAMER) 243 

COST  OF  SMALL  POWER  PLANTS  (EDITORIAL) 245 

CONSTRUCTION  OF  WOODEN  WATER  TANKS  (EDITORIAL)  .     .     .     .     .  246 

PIPE  LINE  CONSTRUCTION  (EDITORIAL) 247 

TRANSPORTATION  OF  GAS  BY  PIPE  LINES  (EDITORIAL) 249 

MAKING  PIPE  JOINTS  (EDITORIAL) 251 


PART  I 
BRICKWORK  AND   CONCRETE 


OF  THE 

UNIVERSITY 

OF 


COST  OF  EARTH  WORK 

(September  19,  1903) 

H.  P.  Gillette,  in  his  recently  published  treatise  on  "Earth 
Work  and  Its  Cost,"  summarizes  various  data  as  to  the  cost  of 
handling  earth  by  picking  and  shoveling  in  the  statement  that 
the  cost  of  excavating  with  pick  and  loading  is  about  40c.  per 
cu.  yd.  for  hard  pan;  20c.  per  cu.  yd.  for  tough  clay;  15c.  per  cu.  yd. 
for  ordinary  clay,  gravel  or  loam,  and  12c.  per  cu.  yd.  for  very 
light  sandy  or  loamy  soils,  wages  being  reckoned  at  15c.  per 
hour  in  all  cases.  After  earth  is  once  loosened  and  shoveled 
upon  a  board  platform,  as  in  casting  in  stages  out  of  a  deep 
trench,  one  man  will  shovel  off  the  boards  all  that  two  men  can 
loosen  and  cast  up.  Although  a  man  can  possibly  cast  earth 
about  12  ft.  vertically  from  floor  to  floor,  it  is  best  to  have  floors 
only  5  to  7  ft.  apart.  The  quantity  of  earth  that  a  man  can 
handle  with  a  shovel  varies  not  only  with  the  character  of  the 
soil,  but  also  with  the  method  of  attack.  If  a  man  is  shoveling 
from  a  face  of  earth  over  a  foot  high,  one  that  he  can  readily 
undermine  with  a  pick,  he  can  load  1.8  cu.  yd.  per  hour  on  an 
average,  but  if  he  is  shoveling  plowed  soil,  where  he  must  use 
more  time  to  force  the  shovel  into  the  soil,  his  output  will  be 
only  about  1.4  cu.  yd.  per  hour.  If  he  is  shoveling  loose  earth 
off  boards  upon  which  it  has  been  dumped  his  output  is  about 
2.5  cu.  yd.  per  hour. 

The  size  of  the  shovel  makes  a  marked  difference  in  the  effi- 
ciency of  the  laborer.  A  small,  round-pointed  shovel  must  be 
used  in  tough  soils,  but  nothing  other  than  large,  square-pointed 
scoops  should  be  used  in  handling  earth  off  boards  or  in  shoveling 
sand,  unless  it  is  to  be  cast  some  distance.  With  a  large,  square- 
pointed  scoop  a  strong  man  can  load  sand  into  a  wheelbarrow  at 
the  rate  of  1  cu.  yd.  in  five  minutes.  Roughly  speaking,  it  takes 
150  to  250  shovels  of  earth  to  make  1  cu.  yd.;  in  casting  into  a 
wagon-box  at  a  good  steady  gait  seven  shovels  are  loaded  per 
minute.  This  is  for  a  vertical  lift  of  about  5  ft.,  but  in  casting 

3 


4  METALLURGICAL  MILL  CONSTRUCTION 

out  of  a  trench  with  a  vertical  lift  of  10  ft.,  only  five  shovels  are 
cast  per  minute.  In  casting  earth  horizontally,  nine  shovels  per 
minute  may  be  done  for  a  5-ft.  throw  and  about  one-half  as 
many  for  an  18-  or  20-ft.  throw.  With  wages  at  15c.  per  hour, 
it  costs  about  5c.  to  carry  a  cubic  yard  10  ft.  in  shovels,  hence 
men  should  be  close  enough  to  the  wagon  they  are  loading,  so  as 
not  to  have  to  take  any  steps  before  casting.  The  further  away 
a  man  is  from  the  wagon  the  fewer  shovels  can  be  cast  in  a  given 
time,  and  as  each  shovelful  is  also  smaller,  a  man  12  or  15  ft. 
away  from  the  wagon  will  load  only  about  one-half  as  much  as 
if  he  were  within  4  or  5  ft.  of  it;  hence  it  does  not  pay  to  crowd 
more  than  six  men  around  a  wagon,  acting  upon  the  idea  that 
quick  loading  saves  money  by  saving  team  time.  Large  square- 
pointed  shovels  should  be  used  wherever  possible.  The  work 
should  be  directed  to  a  face  wherever  possible,  and  a  temporary 
floor  should  be  laid  down  at  the  face,  so  that  earth  picked  down 
will  fall  on  the  floor,  whence  it  can  be  easily  shoveled.  A  high 
face  of  earth  should  be  undermined  with  pick  and  then  wedged 
off  by  driving  in  bars  from  the  top.  Wherever  possible,  in  earth 
work,  men  should  be  paid  by  the  cubic  yard,  not  by  the  day. 


BRICK  MASONRY 

BY  W.  R.  INGALLS 

(August  22,  1903) 

Brick  masonry  is  frequently  paid  for  by  the  cubic  foot,  and 
in  making  estimates  it  is  always  reckoned  thus,  though  the  result 
may  be  converted  into  the  number  of  thousand  brick  required, 
since  brick  are  purchased  by  the  thousand.  The  cost  of  brick 
masonry  depends  upon  the  prices  for  the  material  and  wages  of 
labor,  but  also  to  a  large  extent  upon  its  character;  that  is,  whether 
laid  with  thick  mortar  joints  or  thin  ones,  with  lime  mortar,  lime 
and  cement  mortar,  or  cement  mortar,  and  the  character  of  the 
workmanship  in  laying  the  brick.  In  massive  masonry  laid  with 
mortar  joints  \  to  f  in.  thick,  the  mortar  constitutes  about  20 
per  cent,  of  the  entire  mass.  The  effect  of  thicker  or  thinner 
joints  upon  the  cost  will  be  as  the  relative  price  per  cubic  yard 
of  brick  and  of  the  kind  of  mortar  used.  The  size  of  the  brick 
is  very  important  in  considering  the  cost  of  masonry.  The  brick 
used  in  some  parts  of  the  United  States  measure  only  60  cu.  in., 
while  those  used  in  other  parts  measure  80  cu.  in.  Of  course,  a 
cubic  foot  of  masonry  will  comprise  fewer  of  the  large  brick  than 
of  the  small,  while  the  labor  cost  of  laying  a  thousand  will  be  the 
same  in  each  case.  Moreover,  large  brick  sell  at  the  kilns  where 
they  are  made  at  prices  no  higher  than  the  small  brick  made 
elsewhere.  This  is  because  the  raw  material  is  of  comparatively 
little  value  and  the  labor  in  manufacture  is  largely  determined 
by  the  number  of  pieces  handled  rather  than  their  weight.  Com- 
mon brick  are  rarely  used  otherwise  than  locally  in  the  districts 
which  have  their  own  sizes,  which  is  probably  the  reason  why 
we  have  no  national  standard.  With  fire-brick  the  case  is  differ- 
ent. However,  it  would  appear  that  there  might  be  some  ad- 
vantage in  having  some  uniformity  in  red  brick,  such  as  a  set  of 
standard  sizes,  one  of  which  might  correspond  with  the  standard 
fire-brick,  having  a  volume  of  about  100  cu.  in.  Even  a  large 

5 


6  METALLURGICAL  MILL  CONSTRUCTION 

brick  might  be  desirable  for  some  purposes.  One  of  the  advan- 
tages of  the  Custodis  method  of  chimney  construction  is  the 
reduced  cost  of  laying  the  large,  specially  shaped  brick  used 
therein.  One  of  the  reasons  for  the  use  of  small  brick  as  com- 
pared with  large  ones,  say  16  in.  by  8  in.  by  4  in.,  like  the  Mexican 
adobe,  is  the  better  bond,  but  in  that  respect  I  do  not  suppose  there 
would  be  material  difference  between  brick  of  60  cu.  in.  and  those 
of  100  cu.  in.  Another  reason  for  the  use  of  small  brick  is  the 
thinner  walls  they  permit,  which  is  a  matter  of  some  consequence 
in  the  construction  of  buildings  in  cities  where  land  is  highly 
valuable. 


SAND-LIME  BRICK 

(October  27,  1904) 

According  to  a  paper  prepared  by  S.  V.  Peppel  for  the  United 
States  Geological  Survey,  there  are  in  this  country  at  present 
about  50  plants,  with  a  total  capacity  of  approximately  1,000,000 
bricks  a  day.  The  experience  of  these  plants  indicates  that 
sand-lime  brick  can  usually  be  manufactured  at  a  cost  below 
that  of  common  clay  brick.  Sand-lime  bricks  have  been  in  use 
long  enough,  both  in  this  country  and  in  foreign  countries,  to 
prove  that  when  properly  made  they  have  sufficient  strength 
and  sufficient  water  and  weather  resisting  qualities  to  make  them 
a  safe  building  material. 

The  sand-lime  brick  is  the  natural  outcome  of  improvements 
made  in  the  old  mortar  brick,  which  has  been  known  for  years. 
This  mortar  brick  was  at  first  never  more  than  a  molded  mixture 
of  lime  and  sand  mortar,  which  was  allowed  to  harden  in  the  air. 
About  twenty-five  or  thirty  years  ago,  one  Dr.  Michaelis  patented 
a  process  for  the  hardening  of  mixtures  of  lime  and  sand  by  steam 
under  pressure,  which  is  the  fundamental  principle  on  which  the 
manufacture  of  sand-lime  brick  is  based. 

The  commercial  development  of  the  industry  dates  back  only 
fifteen  years  in  foreign  countries,  and  not  more  than  four  years 
in  the  United  States.  In  1896  Germany  had  only  five  factories 
where  sand-lime  brick  was  made,  but  now  it  has  about  200,  with 
an  actual  annual  output  of  between  350,000,000  and  400,000,000. 
Early  in  1901  a  plant  was  built  in  Michigan  City,  Ind.  In  1902 
about  20  plants  were  in  existence  and  6,000,000  bricks  were 
actually  sold.  Full  data  are  not  obtainable  as  to  the  actual 
output  in  1903,  but  about  20,000,000  bricks  have  been  reported 
as  sold  in  that  year.  Many  of  the  factories  had  just  started,  and 
were  not  manufacturing  to  their  full  capacity  during  the  year. 


CONCRETE  MIXTURE 

(November  18,  1905) 

In  proportioning  a  mixture  for  concrete  or  mortar,  the  engineer 
of  experience  uses  those  proportions  for  different  work  which  he 
has  found  most  effective.  For  important  work,  however,  where 
local  materials  are  used,  it  is  always  well  to  determine  the  pro- 
portions by  actual  test.  This  is  not  troublesome,  nor  is  it  as 
expensive  as  might  be  supposed.  The  instruments  required  for 
the  test  are  an  old  oil  barrel  and  a  dormant  scale.  The  barrel  is 
shoveled  full  of  sand  and  "struck"  to  give  a  flush  top  surface. 
It  is  then  weighed;  and,  after  weighing,  sufficient  water  is  turned 
into  it  to  bring  the  level  of  the  sand  and  water  to  the  top  of  the 
barrel.  It  is  then  weighed  again,  the  difference  in  weight  giving 
the  amount  of  water  required  to  fill  the  voids  in  the  sand.  A 
similar  procedure,  with  crushed  stone  (or  gravel)  and  water, 
gives  the  weight  in  pounds  of  the  water  required  to  fill  the  voids 
in  the  aggregate.  As  the  cement  and  the  cement  and  sand 
matrix  have  not  the  same  specific  gravity  as  water,  for  each  case 
it  is  necessary  to  reduce  the  weight  of  the  water  to  units  of  volume, 
the  result  giving  both  the  volume  of  the  cement  alone  and  also 
that  of  the  matrix  required  to  fill  the  voids  completely.  The 
sand  and  the  aggregate,  when  placed  in  the  barrel,  should  be,  as 
nearly  as  possible,  in  the  same  condition  of  density  as  they  are 
to  be  when  mixed. 


REQUIREMENTS  FOR  CONCRETE 

(March  31,  1904) 

S.  B.  Newbeny,  in  a  paper  read  before  the  Indiana  Engineering 
Society  at  Indianapolis,  Ind.,  Jan.  14,  1904,  stated  that  nowadays 
most  engineers  use  crushed  stone  just  as  it  comes  from  the  breaker, 
without  screening.  However,  good  quartz  gravel  is  better  than 
stone,  since  it  is  harder  (save  in  the  case  of  quartzite  or  trap  rock) 
and  its  round  form  leaves  less  voids.  Round  stone  for  cement 
does  not  make  a  weaker  concrete  than  that  made  with  angular 
material. 

The  proportion  of  voids  is  of  great  importance,  and  insufficient 
attention  is  given  to  it.  The  strength  of  concrete  is  proportional 
to  the  ratio  of  the  percentage  of  cement  to  voids.  Mixtures  in 
which  the  voids  are  filled  to  the  same  extent  will  be  approximately 
equal  in  strength.  Superficial  area  is  also  an  important  factor, 
since  all  surfaces  must  be  coated  with  a  film  of  cement  in  order 
to  produce  proper  adhesion;  the  greater  the  surface  the  greater 
the  quantity  of  cement  required.  Coarser  materials  give  a 
greater  strength  than  fine  materials,  chiefly  for  this  reason. 
Machine  mixing  is  to  be  recommended;  the  sand  and  cement 
should  first  be  mixed,  the  water  should  then  be  added,  and 
finally  the  stone  or  gravel,  which  should  be  previously  well 
wetted. 

Portland  cement  concrete  suffers  no  harm  by  freezing  after 
the  mass  has  fully  set;  its  hardening  is  interrupted,  but  proceeds 
again  without  hindrance  after  thawing.  Damage  is  to  be  feared 
from  frost  before  setting,  however,  especially  if  an  excess  of 
water  be  used. 


LIMESTONE  SCREENINGS  FOR  USE  IN  CONCRETE 

(September  1,  1904) 

The  advisability  of  using  stone-crusher  dust  as  a  substitute 
for  sand  in  the  aggregate  for  concrete  is  the  subject  of  a  good 
deal  of  discussion  among  constructing  engineers.  It  is  of  con- 
siderable interest  to  mining  and  metallurgical  engineers  both 
with  regard  to  structural  work  and  the  possible  sale  of  mill  tailings 
in  favorable  localities. 

G.  J.  Griesenauer  has  stated  (Engineering  News,  July  28,  1904) 
that  tests  in  the  laboratory  of  the  Chicago,  Milwaukee  &  St.  Paul 
railway  have  shown  that  limestone  screenings  are  far  superior  to 
sand  as  a  concrete  aggregate.  Screenings  that  will  at  least  all 
pass  a  4-mesh  sieve  but  not  finer  than  an  8-mesh  are  the  most 
valuable.  A  finer  mesh  than  eight  tends  to  give  a  product 
containing  an  excess  of  impalpable  stone  dust,  especially  if  a 
soft  limestone  be  employed,  while  a  coarser  mesh  than  four  gives 
a  product  of  which  the  handling  is  likely  to  separate  the  coarse 
and  fine  particles  to  some  extent. 

Crusher-run  limestone  would  be  better  than  screened  crushed 
limestone  if  it  were  practicable  to  avoid  a  separation  of  the  coarse 
and  fine,  but  this  being  impossible  the  product  is  not  uniform 
and  therefore  is  likely  to  produce  a  non-homogeneous  concrete. 
Consequently  it  is  preferable  to  screen  the  crushed  stone  and 
keep  the  coarse  and  screenings  separate,  mixing  them  in  the 
proper  proportions  when  required. 

The  quality  of  the  limestone  affects  the  value  of  the  screenings, 
very  soft  stone  being  naturally  inferior  to  the  harder  kinds.  A 
very  soft  limestone  should  not  be  reduced  to  as  fine  screenings  as 
a  harder  stone.  There  is  nothing  to  indicate  that  limestone 
screenings  may  weaken  after  a  certain  age  any  more  than  sand, 
the  particles  in  each  case  being  enclosed  in  cement,  whose  tendency 
is  to  increase  in  strength  with  time. 


10 


-  HE 


UNIVERSITY  } 


RUBBLE  CONCRETE 

(August  22,  1903) 

The  merits  of  rubble  concrete  were  discussed  in  the  Engineering 
News  of  July  16,  1903.  This  is  a  type  of  masonry  that  has  de- 
veloped within  the  last  few  years,  concerning  which  little  has 
yet  been  printed.  The  term  covers  two  classes  of  masonry,  one 
being  concrete  in  which  large  stones  are  imbedded,  and  the  other 
being  rubble  masonry,  in  which  concrete  replaces  ordinary  mortar. 
Concrete  in  which  stones  are  imbedded  is  usually  mixed  very 
wet  and  deposited  in  a  layer  into  which  large  spalls,  or  even 
one-man  stones,  are  rammed  in.  Where  the  spalls  are  flat  bedded, 
a  dry  mixed  concrete  is  sometimes  used,  the  spalls  being  laid  on 
their  flat  faces  and  concrete  rammed  into  the  vertical  joints. 
From  the  last  mentioned  method  it  is  but  a  step  to  the  kind  of 
masonry  in  which  large  irregular  stones  are  deposited  in  the 
walls  by  means  of  a  derrick,  the  joints  between  them  being 
afterward  filled  with  concrete,  preferably  wet  mixture.  The 
advantage  of  this  kind  of  masonry  is,  of  course,  its  economy,  a 
portion  of  the  concrete  being  replaced  by  stone,  which  is  cheap, 
the  saving  varying  according  to  the  proportion  of  cement  used 
in  the  concrete. 

One  of  the  greatest  advantages  of  ordinary  concrete  masonry 
over  ordinary  stone  masonry  is  the  saving  of  labor,  that  of  stone 
cutters  being  eliminated  and  a  less  skilled  class  of  labor  being 
required  for  laying  it,  which  advantages  are  partially  offset  by 
the  necessity  for  crushing  the  stone,  the  necessity  usually  of  pro- 
viding frames  or  molds,  and  the  requirement  of  more  cement  per 
cubic  yard  than  in  other  classes  of  masonry.  The  saving  is  most 
in  comparison  with  cut-stone  masonry.  In  making  comparison 
between  concrete  and  rubble  masory,  the  conditions  are  different. 

Second-class  retaining  walls  on  the  Erie  Canal  required  about 
0.6  barrel  of  portland  cement  per  cubic  yard  of  masonry,  the 
mortar  being  1 : 2,  whereas  a  1:2:5  concrete  (packed  measure) 
required  1.1  barrel  of  cement  per  cu.  yd.  With  cement  at 
$1.60  per  barrel,  this  makes  a  difference  of  about  80c.  per  cu. 

11 


12  METALLURGICAL  MILL  CONSTRUCTION 

yd.  in  favor  of  the  rubble,  in  addition  to  which  there  is  a  sav- 
ing of  about  50c.  per  cu.  yd.  in  the  item  of  forms  and  30c.  a  cu. 
yd.  in  the  item  of  stone  crushing,  making  a  total  of  $1.60  in 
favor  of  the  rubble.  The  cost  of  laying  the  rubble  was  about 
80c.  per  cu.  yd.,  using  high-priced  masons,  as  against  60c.  for 
mixing  and  laying  concrete  by  hand,  or  40c.  by  mechanical 
mixers.  These  costs  of  laying  indicate  clearly  that  ordinary 
rubble  masonry  costs  very  little  more  to  lay  than  does  concrete. 
If  rubble  concrete  be  used  no  skilled  masons  need  be  employed, 
so  that  this  slight  advantage  of  concrete  over  rubble  disappears, 
Engineering  News  argues,  therefore,  that  in  localities  where  stone 
exists  concrete  has  ordinarily  no  economic  advantage  over  stone 
masonry,  except  in  places  where  cut  stone  would  be  used,  and  is 
at  a  positive  disadvantage  as  a  backing  where  appearance  is  of 
no  consequence. 

With  respect  to  the  two  varieties  of  rubble  concrete,  for  small 
retaining  walls  and  for  comparatively  thin  foundations,  the 
method  of  ramming  large  spalls  into  wet  mixed  concrete  is  doubt- 
less to  be  chosen.  In  massive  masonry  where  the  quarries  yield 
large  blocks  of  stone,  the  blocks  should  be  bedded  in  soft  concrete 
and  the  vertical  joints  filled  with  soft  concrete  into  which  spalls 
may  be  rammed.  Where  stone  comes  from  the  quarry  with 
natural  flat  beds,  common  mortar  may  well  continue  to  be  used 
in  the  bed-joints,  the  vertical  joints  being  filled  with  concrete, 
which  will  avoid  dressing  the  stone  at  all.  Where  stone  comes  in 
slabs  easily  broken  by  a  hammer,  or  where  retaining  walls  are 
too  thin  to  permit  the  use  of  large  blocks,  a  soft  concrete  into 
which  the  small  stones  are  rammed  may  be  used.  Where  stones 
come  out  in  large,  tough,  irregular  blocks  a  true  rubble  concrete 
is  probably  the  cheapest,  since  even  with  the  employment  of 
skilled  masons  the  cost  of  laying  is  but  slightly  greater  than 
mixing  and  laying  concrete  with  common  labor. 

As  between  ordinary  concrete  and  rubble  concrete,  if  for  any 
reason  great  strength  is  required,  the  latter  still  has  the  advantage, 
since  if  the  cement  saved  by  imbedding  large  stones  in  the  concrete 
be  used  to  make  a  richer  mortar,  the  rubble  concrete  will  be 
superior  in  strength  to  the  ordinary  concrete,  the  latter  having 
the  weaker  mortar.  The  writer  concludes  his  argument  with  the 
statement  that  a  dollar  wrill  buy  either  more  rubble  concrete  than 
ordinary  concrete,  or  will  buy  a  stronger  masonry. 


CONCRETE  WORK  ABOUT  MINES1 
BY  HENRY  W.  EDWARDS 

(May  19,  1904) 

Concrete,  with  well-proportioned  ingredients,  may  be  safely 
relied  upon  for  a  crushing  strength  of  50  tons  per  square  foot. 
The  ingredients  are  crushed  stone,  sand,  cement  and  water.  The 
stone  is  usually  crushed  to  pass  a  2  to  2.5-in.  ring;  soft  stone,  such 
as  decomposed  porphyry,  is  objectionable,  unless  the  concrete 
is  to  bear  a  light  load.  Slag  broken  to  the  same  size  is  hi  every 
way  suitable;  it  has  only  one  objectionable  ingredient,  namely, 
calcium  sulphide.  The  broken  stone  or  slag  is  not  improved  by 
scresaing.  Jig  tailings,  both  coarse  and  fine,  give  good  results 
when  used  for  sand,  a  mixture  of  all  sizes,  with  0.05  to  0.09  in. 
predominating,  being  best.  Vanner  tailings  and  stamp-battery 
tailings  are  usually  too  fine.  Granulated  slag  is  excellent.  As 
regards  cement,  the  so-called  natural  cements,  while  cheaper  in 
first  cost,  are  usually  less  effective  than  portland  cements.  Any 
doubt  as  to  whether  a  particular  sample  of  cement  is  natural  or 
artificial  can  usually  be  settled  by  testing  for  magnesia.  In  port- 
land  cement  this  is  present  as  an  ace 'dental  impurity,  about  2 
per  cent.,  while  in  natural  cement  it  sometimes  exceeds  10  per 
cent.  Generally  speaking,  concrete  containing  two  parts  of  port- 
land  cement  equals  three  parts  of  natural  cement.  Cement 
should  be  finely  ground,  but  not  to  exceed  100-mesh.  In  testing 
through  wire-cloth  of  this  fineness,  it  is  important  to  see  that  the 
meshes  of  the  sieve  have  not  been  distorted,  allowing  coarser 
material  to  pass.  There  is  a  marked  difference  between  various 
brands  of  portland  cement,  and  these  differences  are  accentuated 
by  age  and  care  in  storage. 

Tests  of  the  tensile  strength  of  cement  are  easily  made  by  an 
ordinary  5-ton  platform  scale,  with  a  good,  strong  screw-jack; 

1  Abstract  of  a  paper  on  "  Concrete  in  Mining  and  Metallurgical  Engineer- 
ing "  read  before  the  American  Institute  of  Mining  Engineers,  February,  1904. 

13 


14  METALLURGICAL    MILL   CONSTRUCTION 

the  pressure  exerted  by  the  screw-jack  is  read  on  the  beam  of  the 
scale  at  the  moment  cracks  appear  on  the  visible  sides  of  the  test 
piece.  A  series  of  mixtures  should  be  made  with  each  brand  of 
cement,  these  mixtures  being  rammed  in  a  wooden  box  9  in. 
square  by  30  in.  long,  and  left  there  for  several  days,  or  weeks, 
until  set.  Many  tests  should  be  made  of  each  series  of  mixtures, 
these  mixtures  ranging  from  one  part  of  cement  with  0.5  part  of 
sand  or  tailings  and  seven  parts  unscreened  crushed  rock,  to  one 
part  of  cement  with  four  parts  of  sand  and  three  parts  of  rock. 

Concrete  may  be  divided  into  three  classes,  according  to  the 
work  required  of  it:  (1)  Strong,  containing  about  15  per  cent, 
of  cement,  for  retaining  walls,  flues,  culverts,  arch  work  in  gen- 
eral, and  foundations  in  wet  places;  (2)  medium,  containing 
about  10  per  cent,  of  cement,  for  engine,  machinery,  stack,  and 
furnace  foundations,  on  good,  dry  ground,  and  for  the  bottoms 
of  flues;  (3)  poor,  containing  about  7  or  8  per  cent,  of  cement 
for  leveling  the  bottoms  of  excavations  previous  to  beginning 
foundations  proper,  and  for  all  foundations  and  below-ground 
work,  where  the  weight  to  be  supported  will  not  exceed  6  tons 
per  square  foot.  Both  medium  and  poor  grades  may  be  diluted 
further  without  diminishing  the  ultimate  strength,  by  using  large 
boulders,  provided  the  concrete  is  properly  tamped. 

In  testing,  it  is  only  necessary  to  work  on  some  of  these  varie- 
ties, usually  the  strong.  One  or  two  blocks  of  each  series  may  be 
tested  at  the  end  of  a  week,  leaving  the  others  to  be  tested  at  the 
end  of  four  weeks.  Any  block  which  stands  a  2-ton  breaking 
test  can  be  pronounced  very  good,  although  a  4-ton  test  is  not 
too  much  to  expect  after  several  months'  drying. 

It  is  to  be  noted  that  two  parts  of  sand,  four  parts  of  crushed 
rock,  and  one  part  of  cement  mixed  together  do  not  give  six 
volumes  of  mixture,  as  the  sand  fills  the  spaces  between  pieces 
of  rock,  and  the  cement  those  between  the  sand  and  rock.  On 
thoroughly  ramming  this  concrete  in  place  it  will  pack  to  a  bulk 
of  four  volumes,  or,  approximately,  the  original  bulk  of  the  crushed 
rock. 

Generally  speaking,  machine  mixing  is  better  than  hand  mix- 
ing, and  it  will  pay  to  install  a  mixer  if  more  than  80  cu.  yd.  is 
required.  An  efficient  mixer  is  a  cubic  wooden  box,  lined  with 
No.  10  sheet  iron,  and  having  an  iron  manhole  at  one  corner. 
The  box  is  mounted  on  two  trunnions,  one  a  piece  of  3-in.  pipe 


BRICKWORK  AND  CONCRETE  15 

through  which  water  is  introduced,  the  other  connected  by  a 
gear-wheel  and  pinion  to  a  hand  crank.  The  box  is  given  a  few 
revolutions  to  mix  the  ingredients  dry,  the  necessary  quantity 
of  water  is  introduced  by  a  hose  and  nozzle  through  the  hollow 
trunnion,  and  then  the  box  is  revolved  as  long  as  desired.  Ideal 
mixing  is  to  have  each  particle  of  rock  and  sand  coated  entirely 
with  cement.  In  hand  mixing  by  shovels,  a  sheet-iron  platform 
lightens  labor. 

The  necessary  amount  of  water  depends  upon  the  climate, 
the  character  of  the  other  ingredients,  and  the  intended  use. 
A  good  rule  is  to  have  the  concrete  so  wet  that  it  will  shake  like 
jelly  when  being  rammed  by  a  heavy  beater,  but  in  shallow  layers, 
as  in  floors,  the  mixture  should  be  much  wetter  than  when  laid 
in  mass,  otherwise  it  will  dry  up  before  chemical  action  begins. 
In  retaining  walls,  it  is  well  to  use  the  mixture  reasonably  dry, 
since  an  excess  of  water,  on  evaporation,  leaves  the  concrete 
porous.  For  tanks,  reservoirs,  etc.,  the  mixture  should  contain 
more  concrete,  and  should  be  more  thoroughly  mixed  and  tamped. 

Concrete  should  be  mixed  as  near  the  point  of  use  as  possible, 
and  a  long  trip  in  a  wheelbarrow  is  to  be  avoided.  Where  it 
must  be  handled  by  wheelbarrow,  it  is  best  to  dump  the  material 
on  a  small  platform  and  shovel  it  over,  before  putting  it  in  place. 
Care  should  be  taken  that  all  parts  are  equally  wet;  otherwise 
some  portions  of  the  work  may  dry  before  others,  and  thus  cause 
cracks. 

For  foundations  and  walls,  the  material  should  be  laid  in  layers, 
not  over  6  in.  deep,  to  get  the  full  benefit  of  beating.  A  conven- 
ient beater  is  made  of  an  iron  casting  6  in.  square,  with  a  handle 
of  1  or  1.5-in  pipe  about  5  ft.  long,  the  whole  weighing  20  to 
25  Ib.  Each  layer  should  be  put  on  before  the  previous  one  is 
set,  and  not  more  than  a  half-hour  should  elapse  between  mixing 
and  depositing.  It  is  advantageous  to  have  the  work  continue 
day  and  night,  but,  if  interrupted,  the  layer  that  has  set  should 
be  cleaned  and  wetted  first  with  water,  and  then  with  thin  cement 
grout,  before  adding  a  new  layer.  As  vertical  joints  in  a  wall 
are  less  weakening  than  horizontal  ones,  a  long  retaining  wall 
may  be  divided  into  panels,  each  of  a  size  that  can  be  completed 
in  a  day's  work. 

The  making  of  cribs  or  forms  permits  much  ingenuity.  They 
should  be  stiff  enough  to  stand  the  beating  of  the  concrete,  and 


16  METALLURGICAL  MILL  CONSTRUCTION 

so  arranged  that  the  timber  may  be  used  repeatedly.  Plain  2-in. 
planks,  with  straight  planed  edges,  are  better  than  tongue-and- 
groove  boards.  In  filling  behind  such  a  crib  the  concrete  should 
never  be  dumped  from  a  height,  else  the  mortar  and  stone  will 
separate.  In  a  deep  excavation  the  concrete  may  be  lowered 
in  a  tub  or  bucket  and  dumped  in  place. 

The  time  required  for  seasoning  varies  with  the  climate  and 
the  season  of  the  year.  In  summer,  or  in  a  dry  winter  climate, 
the  action  is  rapid,  and  a  covering  of  moist  sand  may  be  necessary 
to  prevent  too  rapid  hardening.  In  northern  climates  with  cold 
winters,  concrete  laid  in  the  fall  will  not  be  really  solid  until 
warm  weather  sets  in.  Where  the  load  is  to  be  applied  gradually, 
as  in  a  retaining  wall  filled  from  behind,  loading  may  begin  after 
a  week  or  two  of  warm  weather.  For  thin  work,  such  as  floors 
and  flues,  a  few  days  may  suffice;  an  engine  foundation  can  be 
used  after  a  week  or  two.  In  heavy  masses,  hardening  and 
seasoning  may  go  on  for  many  months. 

For  work  under  water,  a  home-made  iron  funnel,  with  a  stem 
long  enough  to  reach  bottom  and  cut  off  as  necessary,  is  useful. 
By  resting  the  outlet  of  the  funnel  on  the  bottom,  filling  the  stem 
and  hopper  with  concrete,  lifting  a  little  and  moving  as  desired, 
the  concrete  can  be  spread  evenly.  In  running  water,  a  coffer- 
dam, slightly  higher  than  the  depth  of  water,  may  be  made  out 
of  a  double  layer  of  boards,  with  a  layer  of  tarred  roofing  paper 
between.  The  ground  upon  which  the  foundation  is  to  rest  is 
leveled  roughly,  and  the  coffer-dam  is  carefully  sunk  into  position 
by  loading  it  with  concrete.  This  is  much  cheaper  than  pumping 
out  the  water  and  laying  the  concrete  in  the  usual  manner;  it  is 
cheaper  also  than  sheet  piling. 

It  is  difficult  to  give  any  definite  figures  of  cost,  owing  to  the 
great  variation  in  the  price  of  the  ingredients  in  different  localities  ; 
also,  the  size  of  the  work  is  a  factor.  Presuming,  however,  that 
the  materials  are  delivered  in  railroad  cars  convenient  to  the 
work,  I  find  that  an  average  cost  covering  unloading,  mixing, 
arranging  platform,  placing  and  beating  is  approximately  equiva- 
lent to  a  cubic  yard  of  structure  per  man  per  day.  This  covers 
incidentals,  such  as  wear  and  tear  on  tools,  etc.,  but  not  the  cost 
of  cribs,  excavations,  scaffolding,  lumber,  etc.  The  cheapest 
piece  of  work  of  which  I  have  record  is  a  retaining  wall  16  ft. 
high,  92  ft.  long,  and  3  ft.  thick  at  the  base,  tapering  to  20  in. 


BRICKWORK  AND  CONCRETE  17 

at  the  top.  Jig  tailings  and  picking-belt  rock  available  on  the 
spot  were  used,  while  cement  cost  $2.15  per  bbl.,  lumber  $14  per 
1000  ft.,  and  wages  were  15c.  an  hour.  The  total  cost  was  22c. 
per  cu.  ft.,  including  supervision.  A  large  engine  foundation  of 
hand-broken  slag,  granulated  slag  and  cement  cost,  including 
crib,  $7.75  per  cu.  yd.  of  finished  work. 


CONCRETE  FOUNDATIONS  AND  FLOORS  * 

In  construction,  the  men  executing  masonry  or  concrete  work 
will  often  go  to  considerable  trouble  to  secure  screened  sand, 
irrespective  of  the  really  positive  advantage  that  is  to  be  obtained 
in  most  cases  by  using  unscreened  material.  Sand  that  will  pass 
an  8-mesh  sieve  ought  never  to  be  screened  except  for  the  highest 
class  brick  or  cut-stone  (coursed)  masonry. 

Well  made  1 : 5  portland  cement  concrete,  of  good  standard 
gravel  or  limestone  screening,  will  have  a  compressive  strength 
at  four  weeks  of  over  2000  Ib.  per  sq.  in.;  and  at  one  year,  over 
3000  Ib.  Tests  made  at  the  Case  School  of  Science  showed  that 
3-in.  cubes  of  £:  6  portland  cement  and  gravel  concrete  had  a 
compressive  strength  of  3200  Ib.  per  sq.  in.  at  six  weeks,  a  sp.  gr. 
of  2.17,  and  an  absorption  of  water  of  4.16  per  cent.  Similar  cubes 
of  1J  parts  cement,  J  hydrated  lime,  and  6  of  sand  and  gravel 
had  a  strength  of  3880  Ib.,  a  sp.  gr.  of  2.18,  and  an  absorption 
of  4.10.  Cubes  of  1J  parts  of  cement  and  6  of  limestone  screening, 
poured  in  a  porous  mold,  had  a  strength  of  2000  Ib.,  a  sp.  gr.  of 
2.5,  and  an  absorption  of  5.04. 

The  coefficient  of  expansion  of  concrete,  of  the  proportions 
1:  2:  4,  by  heat,  has  been  determined  as  0.0000055  for  1  deg.  F., 
which  is  almost  the  same  as  that  of  untempered  steel,  which  is 
0.0000060. 

In  proportioning  the  material,  when  the  mixture  is  by  volume 
and  the  mixing  is  done  by  hand,  a  bottomless  box  will  serve  as 
a  simple  and  effective  measure.  If  the  box  is  made  of  2Xl2-in. 
plank,  3  ft.  square  inside,  the  dimensions  are  most  satisfactory. 
Such  a  box,  once  even-full  of  sand,  and  evenly  filled  three  times 
with  the  aggregate,  with  four  bags  of  cement,  will  make  just 
1  cu.  yd.  of  concrete  (of  the  proportion  1 — 2 — 6),  in  place.  The 
cement,  of  course,  is  to  be  mixed  with  the  sand  before  adding 
the  aggregate.  Four  short  pieces  of  wood  are  spiked  fast  to  the 
box,  serving  as  handles. 

1  An  arrangement  of  miscellaneous  notes  from  the  Engineering  and  Min- 
ing Journal,  Vol.  LXXX. 

18 


BRICKWORK  AND  CONCRETE  19 

Concrete,  made  of  the  "  run-of-crusher "  rock,  without  the 
addition  of  sand  has  been  successfully  used;  when  the  particles, 
known  as  "dust,"  are  sufficiently  clean  and  sharp,  the  results 
are  even  better  than  when  sand  is  used. 

Concrete  made  of  broken  or  crushed  brick  instead  of  stone 
gives  excellent  results  for  some  purposes ;  but  it  always  requires  a 
larger  proportion  of  cement  than  when  less  porous  material  is 
used. 

The  writer  once  saw  a  gang  of  men  mixing  concrete  by  hand, 
with  pointed  shovels.  This  statement  may  not  bring  to  mind 
the  actual  heinousness  of  the  crime  against  good  practice  that 
such  work  becomes,  but  when  one  considers  that  square-toed 
shovels  would  pick  up  and  mix  with  the  aggregate  the  wet 
cement  and  sand  (the  most  costly  ingredient  of  the  batch)  that 
the  pointed  or  round-toed  shovel  allows  to  escape,  the  term  does 
not  seem  too  strong.  The  square-toed  D-handled  shovel  is  about 
the  only  one  that  is  suited  for  such  work  as  this,  and  should 
always  be  used  in  preference  to  any  other  form.  When  mixing 
is  done  by  hand,  the  mixing  board  should  always  be  used,  unless 
a  smooth,  impervious  floor  may  be  at  hand.  It  seems  needless 
to  caution  against  mixing  on  the  bare  ground,  and  yet  it  is 
done  more  often  than  one  would  expect,  through  ignorance  or 
carelessness.  The  amount  of  cement  that  is  lost  in  this  practice 
is  beyond  calculation,  and  criminal  from  the  standpoint  of 
economics. 

For  floors  a  mixture  of  1  part  portland  cement,  3  parts  clean, 
sharp  sand  and  5  parts  of  broken  stone  that  will  pass  through 
a  2-inch  ring  is  recommended.  There  should  be  a  finishing  coat 
i  to  1  in.  thick,  according  to  amount  of  use  of  the  floor,  and  this 
may  be  made  of  various  proportions,  from  1  of  cement  and  i  of 
sand,  to  1  of  cement  and  2  of  sand,  the  mixtures  with  the  larger 
amount  of  sand  standing  the  wear  of  traffic  best,  and  those  richest 
in  cement  being  most  nearly  impervious  to  water.  Trowel  finish 
usually  makes  a  floor  quite  impervious.  Expansion  joints  must 
be  provided  if  there  is  likely  to  be  considerable  change  in  tem- 
perature of  the  floor,  or  steel  mesh  reenforcing  may  be  used. 
Such  a  floor  is  not  ready  to  use  in  less  than  a  week  after  it  is 
fully  completed,  and  longer  time  is  desirable.  It  will  set  suffi- 
ciently to  bear  weights  in  less  time,  but  will  not  stand  wear. 
Failure  may  occur  even  with  the  utmost  care  and  the  best  ma- 


20  METALLURGICAL  MILL  CONSTRUCTION 

;terials.  It  is  always  advisable  to  keep  the  upper  surface  damp 
while  the  material  is  setting. 

Concrete  floors  are  not  suitable  for  use  about  electrolytic  or 
lixiviating  plants  because  acid  solutions  attack  and  gradually 
disintegrate  the  cement;  but  this  action  can  be  largely  prevented 
by  asphalt  coatings. 

In  placing  concrete  in  two  or  more  layers,  which  is  the  usual 
practice  in  floor  or  sidewalk  work,  it  is  desirable  to  place  the  top 
layer  before  the  first  is  set,  or,  in  case  this  rule  cannot  be  followed, 
a  firm  bond  is  secured  by  thoroughly  scratching  the  first  layer 
while  it  is  soft. 

Care  should  be  taken  during  hot  weather  to  prevent  the  rapid 
drying  of  concrete.  It  should  be  protected  from  the  sun  and 
occasionally  sprinkled  with  water;  it  is  a  good  plan  to  cover  the 
smaller  masses  with  a  wet  cloth.  This  will  prevent,  to  a  large 
extent,  the  formation  of  "hair  cracks,"  or  crazing. 


PART  II 
BUILDING  CONSTRUCTION 


DESIGN  OF  MILL  BUILDINGS 

(March  31,  1904) 

The  best  modern  practice  inclines  toward  single-floor  buildings 
for  shop  and  factory  purposes;  the  advantages  of  this  type  over 
multiple  story  buildings  are  better  light,  better  ventilation,  easier 
heating,  cheaper  foundations,  absence  of  vibration,  cheaper  floors, 
better  supervision,  cheaper  handling  of  material,  cheaper  construc- 
tion, less  danger  of  damage  by  fire,  and  better  ability  to  make 
extensions.  The  floors  may  be  laid  with  cinder,  or  with  brick 
on  a  gravel  or  concrete  foundation,  but  in  buildings  where  men 
have  to  work  at  machines  the  favorite  floor  is  plank  on  a  founda- 
tion of  cinder,  gravel,  or  tar  concrete.  Concrete  or  cement  floors 
are  used  in  many  cases  with  good  results,  but  are  unsatisfactory 
where  men  have  to  stand  at  benches  or  machines. 

Buildings  in  which  men  are  to  work  should  be  well  lighted. 
It  is  now  the  common  practice  to  make  as  much  of  the  roof  and 
sides  of  a  transparent  or  translucent  material  as  practicable;  in 
many  cases  50  per  cent,  of  the  roof  surface  is  made  of  glass,  while 
skylights  equal  to  25  or  30  per  cent,  of  the  roof  surface  are  very 
common.  Windows  and  skylights  directly  exposed  to  the  sun- 
light should  be  curtained  with  white  muslin  cloth,  which  admits 
much  of  the  light  and  prevents  the  glare  and  excessive  heat  in 
summer,  which  are  objectionable.  The  saw-tooth  type  of  roof 
with  the  shorter  and  glazed  tooth  facing  the  north  gives  the 
best  light,  and  is  now  coming  into  general  use.  The  principal 
difficulty  in  saw-tooth  roof  construction  is  the  arrangement  of 
satisfactory  gutters  and  the  liability  of  snow  to  drift  on  the  roof. 

Plain  glass,  wire-glass  and  ribbed  glass  are  used  for  glazing 
the  windows  and  skylights  of  factory  buildings.  Ribbed  glass 
should  be  placed  with  the  ribs  vertical,  since  otherwise  the  glass 
gives  a  glare  which  is  very  trying.  Wire  netting  should  always 
be  stretched  under  skylights  of  ordinary  glass,  to  prevent  accidents 
from  falling  glass  in  case  of  breakage. 

23 


COST  OF  A  SINGLE-FLOOR  MILL 

(April  26,  1902) 

A  workshop,  120  by  180  ft.,  with  a  single  floor  at  ground 
level,  recently  erected  in  Massachusetts,  cost  65c.  per  square 
foot.  The  framing  conformed  to  the  principles  of  standard  mill 
construction.  The  roof  was  three-inch  plank,  tarred  and  graveled. 
The  sides  were  closed  in  with  windows  of  translucent  glass,  hinged 
from  the  top  and  swinging  outward,  each  window  filling  a  bay 
down  to  about  three  feet  from  the  ground.  Below  the  windows 
the  sides  were  concrete,  laid  on  expanded  metal.  Additional 
light  was  provided  by  monitors  in  the  roof.  The  floor  consisted 
of  four  inches  of  concrete,  surfaced  smoothly,  laid  on  eight  inches 
of  clinker,  well  packed  down. 


In  making  templets  for  bearings  under  steel  beams,  bluestone 
curbing  is  cheaper  by  far  than  the  cut  stone  commonly  used, 
and  is  sufficiently  smooth  and  even,  in  most  cases,  to  answer  the 
purpose.  For  beams  of  12-in.  depth  and  over,  however,  it  is 
better  to  use  thicker  material  than  the  (nominal)  4-in.  curbing. 


In  the  construction  of  brickwork,  the  most  intricate  problems 
can  be  solved  by  the  simple  expedient  of  building  a  model.  This 
is  not  as  difficult  or  expensive  as  one  might  suppose.  Soap,  cut 
into  blocks  J  by  £  by  1  in.  is  the  most,  satisfactory  material  for 
such  models;  the  ordinary  yellow  laundry  variety  gives  good 
results  and  is  the  least  expensive  to  use.  Where  much  of  this 
work  is  to  be  done,  the  best  way  to  cut  the  blocks  is  by  a  case- 
knife,  guided  by  saw-cuts  in  the  cutting  board,  somewhat  in  the 
manner  of  a  carpenter's  miter-box 


24 


LIGHTING  OF  WORKSHOPS 

(September  5,  1903) 

Good  light  in  a  factory  or  workshop  is  an  important  considera- 
tion in  connection  with  the  obtaining  of  the  maximum  efficiency 
of  the  labor,  but  we  know  of  no  rule  as  to  the  proper  proportioning 
of  the  windows  to  floor  space,  etc.  According  to  C.  Zimmermann, 
M.D.,  in  the  Journal  of  the  American  Medical  Association,  Jan.  19, 
1901,  a  school-room,  to  be  thoroughly  well  lighted,  should  have 
30  sq.  in.  of  glass  per  square  foot  of  floor,  or  1  sq.  ft.  of  glass  to 
5  sq.  ft.  of  floor;  the  window  sill  should  be  at  least  40  in.  above 
the  floor  in  order  to  prevent  glare  from  below,  and  the  walls  of 
the  building  should  be  chamfered  at  the  windows,  on  the  inside. 
These  data  may  be  a  guide  in  factory  design,  but  we  conceive 
there  are  many  other  factors  to  be  considered,  such  as  hight  of 
the  stories,  relation  between  floor  space  and  length  or  width  of 
the  room,  exterior  obstructions  to  light,  etc.  A  one-story 
building  200  by  200  ft.  might  have  windows  10  ft.  high  all  the 
way  round  the  outside,  giving  a  ratio  of  glass  to  floor  of  approxi- 
mately 1  to  5,  and  yet  not  be  thoroughly  well  lighted.  Such  a 
building  would  doubtless  be  designed  with  illumination  from 
above,  either  by  means  of  monitor  sky-lights,  or  by  a  roof  con- 
struction of  the  saw-tooth  type.  The  character  of  the  glass  used 
in  the  windows  is  also  a  factor.  We  find  in  our  notebook  the 
statement,  authority  unknown,  that  light  is  diminished  13  per 
cent,  by  the  interception  of  polished  plate  glass  |  in.  thick,  30 
per  cent,  by  rough  cast  plate  }  in.  thick,  53  per  cent,  by  rough, 
rolled  glass  \  in.  thick,  and  22  per  cent,  by  32-oz.  sheet  glass. 


25 


OF  THE 

(   UNIVERSITY  ) 

Of 


LIGHTING  OF  MILL  BUILDINGS 4 
BY  C.  A.  RAYMOND 

(August  5,  1905) 

It  is  not  until  recently  that  the  lighting  of  mill  buildings  has 
occupied  the  attention  of  designers  in  this  country  to  any  great 
extent,  but  rapid  strides  are  now  being  made  in  the  direction  of 
better  diffusion.  The  area  of  glass  in  most  buildings  has  been 
largely  increased,  in  some  instances  to  excess.  The  area  of  glass 
should  be  limited  by  the  following  considerations:  (1)  In  mill 
buildings  where  double  glazing  is  too  expensive  the  heating  is 
rendered  more  difficult  by  an  increase  of  glass  surface.  (2)  An 
excess  of  glass,  when  exposed  to  direct  sunlight,  is  apt  to  make 
the  building  excessively  warm,  unless  rendered  translucent  by  a 
coating  of  white  lead  or  similar  preparation.  (3)  The  expense  of 
replacing  broken  glass  in  some  classes  of  shops  may  be  considerable, 
though  this  may  be  obviated  by  proper  protection. 

The  location  of  a  building,  with  respect  to  the  points  of  the 
compass,  largely  affects  the  quality  of  the  lighting.  North  light 
is  the  best,  because  of  its  steadiness.  It  is,  however,  not  so 
important  to  have  a  large  quantity  of  light  as  to  have  it  well 
diffused.  These  facts  have  developed  the  saw-tooth  roof,  a 
European  type,  which  is  now  being  used  in  some  very  good 
buildings  in  this  country.  There  are  several  strong  objections 
to  it,  but  much  also  to  be  said  in  its  favor.  It  is  not  difficult  to 
design  a  building  so  that  this  roof  may  be  used  no  matter  how  the 
land  may  lie  with  reference  to  the  points  of  the  compass,  the 
worst  case  being  when  the  designer  is  compelled  to  run  his  building 
toward  the  quarter  points.  In  locations  where  much  snow  falls, 
this  type  of  roof  should  be  avoided;  but  where  snows  are  infre- 
quent and  not  usually  deep,  it  offers,  as  a  rule,  a  very  satisfactory 
method  of  lighting,  though  some  means  must  often  be  provided 
for  warming  the  gutters  to  dispose  of  the  snow  and  ice  rapidly. 
Gutters  should  be  specially  large  or  leakage  is  apt  to  occur. 

1  Abstract  of  a  paper  read  before  the  Toledo  Society  of  Engineers. 

26 


BUILDING  CONSTRUCTION  27 

As  far  as  possible,  roof  lights,  to  be  most  efficient,  should  be 
placed  normal  to  the  direction  of  the  source  of  light.  This  is 
illustrated  by  the  usual  form  of  saw-tooth,  which  is  inclined  at 
an  angle  of  20  deg.  to  the  vertical. 

Ribbed  glass  has  done  much  to  improve  the  quality  of  light 
in  mill  buildings.  It  serves  as  a  cheap  substitute  for  prismatic 
glass,  and,  owing  to  its  great  diffusive  qualities  and  low  cost,  is 
extensively  used  in  both  skylights  and  windows.  It  is  no  doubt 
most  effective  for  windows  when  the  ribs  run  horizontally,  but 
shopmen  who  have  worked  by  it  without  shades  find  the  glare 
from  it  troublesome  to  the  eyes  when  exposed  to  direct  sunlight. 
This  difficulty  may  be  effectively  obviated  by  shades,  but  these 
are  ordinarily  considered  too  expensive.  With  the  use  of  this 
glass  the  central  part  of  the  room  gains  a  large  part  of  that  light 
which  in  the  case  of  ordinary  glass  falls  on  the  floor  near  the 
windows. 

Translucent  fabric  is  a  fairly  low-priced  and  otherwise  good 
substitute  for  glass.  Being  translucent  and  not  transparent;  it 
is  good  for  skylights. 

In  order  to  aid  in  the  diffusion  of  light,  the  interior  of  the 
building  may  be  painted  white,  simple  whitewash  being  frequently 
employed. 

Condensation  is  a  point  to  be  reckoned  with  in  skylights,  but 
is  usually  cared  for  by  means  of  gutters  placed  at  intervals  under- 
neath the  glass.  Many  kinds  of  roofing,  also,  are  troublesome  on 
this  account. 


HOLLOW  BRICK  FOR  MILL-BUILDING  CONSTRUCTION 

(March  31,  1904) 

Mill-buildings  for  machine  shops,  foundries,  metallurgical 
works  and  similar  purposes  are  commonly  constructed  of  steel 
framework,  closed  in  with  corrugated  iron;  or  of  brick  walls  and 
steel  roof.  The  latter  construction  is  the  more  expensive,  but  it 
is  also  the  more  substantial,  and  possesses  other  advantages.  A 
combination  of  the  two  kinds  of  construction  has  also  come  into 
extensive  use,  viz.:  a  self-supporting  steel  frame  with  curtain 
walls  of  brick  or  concrete  laid  in  between  the  steel  columns; 
these  walls  can  be  made  much  thinner  than  would  be  otherwise 
required.  A  more  recent,  improvement  is  the  construction  of 
such  curtain  walls  of  hollow  brick  or  tile,  which  effects  a  large 
saving  in  material  and  labor,  and  has  been  proved  to  be  an  entirely 
practicable  system  of  construction,  an  example  of  which  is  to  be 
seen  in  the  tank-house  of  the  American  Smelting  and  Refining 
Company's  works  at.  Perth  Amboy,  N.  J. 

This  is  a  building  350  ft.  long,  200  ft.  wide,  and  24  ft.  6  in. 
high.  The  roof  is  supported  by  columns  (12-inch  I-beams) 
spaced  16  ft.  apart,  centers.  The  spaces  between  the  columns 
wrere  laid  up  with  hollow  tile,  12  by  8  by  4  in.7  set  so  as  to  make 
a  wall  4  in.  thick.  Between  every  second  course  of  blocks  a  strip 
of  band  iron,  1  in.  by  J  in.,  was  laid  in  the  cement  joint  and 
secured  to  the  I-beams  by  1  in.  by  y^-in.  rivets.  A.  Muller,  in 
Insurance  Engineering,  April,  1902,  compares  the  cost  of  this 
construction  with  that  of  a  solid  brick  wall,  1.5  brick  thick,  as 
follows : 

Solid  brick:  565  M  of  brick  (21  per  sq.  ft.  of  wall)  @  $5.75 
per  M,  $3250.  Cement,  sand,  and  labor  of  laying,  @  $8.57  per 
M,  $4841;  total,  $8091. 

Hollow  brick:  Contract  price  delivered,  including  band  iron, 
was  $1800;  cement,  sand,  and  labor,  @  6c.  per  sq.  ft.,  $46.20 
per  M,  came  to  $16.17;  total,  $3426. 

The  difference  in  favor  of  the  hollow  blocks  was,  therefore, 

28 


BUILDING  CONSTRUCTION  29 

$4665,  but  this  does  not  take  into  account  the  cost  of  the  steel 
columns  and  their  erection.  The  weight  of  the  565  M  of  common 
brick  was  1130  tons,  while  that  of  the  35  M  of  hollow  blocks  was 
only  280  tons. 

All  of  the  buildings  at  the  new  plant  of  the  Barber  Asphalt 
Paving  Company  in  New  Jersey  have  been  constructed  on  a 
similar  system,  in  this  case  called  the  Phoenix  system,  which  has 
been  patented  by  Henry  Maurer  &  Son,  of  New  York.  The 
hollow  blocks,  12  by  8  by  4  in.,  are  made  of  hard-burned  terra- 
cotta. The  wall  panels  are  the  spaces  between  I-beam  columns 
set  15  ft.  apart,  centers.  The  wall  is  reinforced  by  a  strip  of 
band  iron  laid  in  cement  between  each  course  of  blocks.  The 
comparative  cost  of  a  wall  of  common  red  brick  and  one  of  the 
Phoenix  hollow  tile,  at  prevailing  prices  in  the  neighborhood  of 
New  York  City,  is  estimated  in  Insurance  Engineering,  October, 
1903,  as  follows: 

Solid  brick:  A  mason  working  8  hours,  at  65c.  per  hour,  with 
a  helper  at  37. 5c.,  will  lay  1200  brick,  making  the  labor  cost 
$6.33  per  M.  The  brick  cost  $7.25  per  M,  and  1  bbl.  of  cement, 
at  $2.50,  1  bbl.  of  lime,  at  $1.25,  and  1  cu.  yd.  of  sand,  at  $1.25, 
are  required  for  the  mortar,  making  the  total  cost  of  the  brick 
in  the  wall  $18.58  per  M.  Reckoning  21  brick  per  cu.  ft.,  or  per 
sq.  ft.,  if  the  wall  be  12  in.  thick,  the  cost  of  100  sq.  ft.  of  wall  is 
$39.02,  or  39c.  per  sq.  ft. 

Hollow  brick:  The  construction  of  a  4-in.  wall  15  ft.  high, 
with  I-beam  columns  15  ft.  apart,  requires  for  each  225  sq.  ft. 
one  6-in.  I-beam,  weighing  227.25  Ib.  (14.75  Ib.  per  foot),  350  ft. 
of  1-in.  by  yV""1-  Dand  iron>  weighing  0.09  Ib.  per  foot,  330 
hollow  blocks,  12  by  8  by  4  in.,  1.5  bbl.  cement,  and  0.75  cu.  yd. 
of  sand.  The  cost  of  this  material  is  as  follows:  227.25  Ib.  of 
I-beam,  at  2.65c.,  $6.02;  31.25  Ib.  band  iron,  at  3.2c.,  $1;  1.5 
bbl.  cement,  at  $2.50,  $3.75;  0.75  cu.  yd.  of  sand,  at  $1.25, 
94c.;  330  hollow  blocks,  at  8.18c.,  $27;  total,  $38.71;  equiva- 
lent to  about  $1.55  per  sq.  yd.  and  17. 2c.  per  sq.  ft.  for  material 
alone.  A  mason,  working  8  hours  at  65c.  per  hour,  with  a 
helper  at  37.5c.  per  hour,  will  lay  220  blocks,  making  150  sq. 
ft.;  wherefore  the  labor  cost  is  about  5.5c.  per  sq.  ft.,  and 
the  total  cost  of  the  wall  is  22. 7c.  per  sq.  ft.,  exclusive  of  the 
cost  of  scaffolds,  which  will  be  the  same  in  either  case. 

A  common  red  brick  weighs  about  4  Ib.,  while  a  hollow  brick, 


30  METALLURGICAL  MILL  CONSTRUCTION 

12  by  8  by  4  in.,  weighs  16  Ib.  Inclusive  of  the  iron  and  steel, 
the  ratio  of  weight  of  a  4-in.  hollow  brick  wall  to  a  12-in.  solid 
wall  is  about  1 : 3.3,  which  permits  a  saving  to  be  made  in  the 
foundations.  The  other  advantages  of  hollow  walls  are  adequate 
strength,  thorough  fireproof  character  and  quickness  of  erection. 
For  many  kinds  of  work,  such  a  building,  with  a  roof  of  red  clay 
tiles,  makes  an  ideal  construction.  A  recent  invention  is  the 
manufacture  of  glass  tiles,  which  can  be  laid  in  connection  with 
red  clay  tiles  so  as  to  give  admirable  lighting  from  above. 


NEW  USES  OF  CONCRETE  IN  BUILDING  CONSTRUCTION 

(October  24,  1903) 

One  of  the  important  factors  in  connection  with  the  recent 
remarkable  development  of  the  American  cement  industry  is  the 
increasing  attention  which  is  being  directed  to  the  use  of  concrete 
in  building  construction,  chiefly  in  the  form  of  reinforced  concrete. 
The  ease  with  which  concrete  can  be  molded  into  monolithic 
forms,  its  great  strength,  the  absolute  protection  which  it  gives 
to  iron  and  steel  imbedded  in  it,  and  its  fireproof  qualities,  which 
have  been  established  beyond  doubt,  combine  to  make  it  a  ma- 
terial of  the  highest  value.  The  idea  of  reinforced  concrete,  i.e., 
concrete  strengthened  by  light  steel  bars  or  wire  netting,  or 
expanded  metal  imbedded  in  it,  was  first  developed  in  France  by 
J.  Monier,  and  early  found  application  in  metallurgical  engineering 
in  the  construction  of  dust-  and  fume-settling  flues.  These  have 
become  standard  practice,  and  are  to  be  seen  at  nearly  all  of  the 
most  recently  constructed  lead  and  copper  smelteries  in  the 
United  States,  notably  at  the  new  plant  of  the  American  Smelting 
and  Refining  Company,  at  Murray,  Utah.  In  general  building  con- 
struction the  Monier  system  has  been  more  generally  adopted  in 
France  and  Germany,  but  during  the  last  few  years  its  use  has 
become  considerable  in  the  United  States. 

There  are  a  number  of  patented  modifications  of  the  Monier 
system.  Among  these  may  be  named  the  Ransome,  in  which 
twisted  steel  bars  are  used;  the  Hennebique,  using  round  steel 
bars  and  a  certain  style  of  stirrups  to  resist  shearing;  the  De 
Valliere,  differing  from  the  Hennebique  principally  in  the  style 
of  the  stirrups  employed;  the  Thatcher,  using  strengthening  bars 
with  projections  in  connection  with  the  concrete;  the  Columbian, 
using  special  forms  of  rolled  steel;  the  Roebling,  in  which  a  netting 
and  rods  are  used,  principally  as  centers  for  concrete  arches;  the 
Expanded  Metal  system,  used  only  for  slabs  and  not  for  beams; 
and  numerous  other  less  well-known  systems.  A  recently  intro- 
duced fireproof  roofing  material  is  "ferroinclave,"  made  of  sand 

31 


32  METALLURGICAL  MILL  CONSTRUCTION 

and  cement  in  the  form  of  slabs  1.5  in.  thick,  in  the  center  of 
which  is  incorporated  a  sheet  of  steel,  corrugated  deeply  in  a 
peculiar  manner. 

The  most  ambitious  example  of  reinforced  concrete  construc- 
tion is  the  now  famous  Ingalls  building  at  Cincinnati,  which  has 
attracted  deep  engineering  interest.  This  is  a  16-story  building, 
which  is  practically  a  monolith  of  reinforced  concrete  (Ransome 
system).  It  is  50  by  100  ft.  in  area  and  210  ft.  in  height.  The 
concrete  used  in  its  construction  is  composed  of  1  part  portland 
cement,  2  parts  sand,  and  4  parts  of  hard  limestone  of  1  in.  size. 

Another  system  of  construction  that  is  extending  to  a  marked 
degree  is  the  use  of  concrete  blocks.  An  example  of  this  kind  of 
construction  is  the  method  of  the  American  Hydraulic  Stone 
Company,  of  Denver,  Colo.,  described  in  the  Engineering  News 
of  Sept.  17,  1903.  Walls  built  of  concrete  blocks  are  usually 
hollow,  and  may  be  of  "one-piece"  or  " two-piece"  construction. 
In  the  former  case  each  block  is  hollow,  and  its  width  is  equal  to 
the  thickness  of  the  wall.  In  the  latter  case  the  blocks  are 
approximately  of  T-shape  in  plan,  set  on  edge,  so  that  two  blocks 
form  the  inner  and  outer  faces  of  the  wall,  their  ribs,  12  in.  apart, 
serving  as  cross-bonds.  The  American  Hydraulic  Stone  Company 
is  exploiting  the  latter  system.  The  blocks  are  usually  9  by  24  in. 
on  the  face,  the  ribs  varying  according  to  the  thickness  of  wall 
required.  The  regular  blocks  weigh  38  Ib.  each,  and  a  wall  built 
of  them  contains  52  per  cent,  open  space.  The  blocks  are  molded 
from  a  mixture  of  1  part  cement  to  6  or  8  parts  of  f-in.  crushed 
stone  under  hydraulic  pressure  of  30  to  35  tons.  For  an  ordinary 
3-story  building,  walls  of  this  construction  9  in.  thick  are  sufficient. 
For  a  higher  building,  or  for  heavy  construction,  the  walls  of  the 
lower  stories  should  be  12  or  14  in.  thick,  or  a  10-in.  wall  may  be 
used,  some  of  the  hollow  spaces  being  filled  with  concrete  to  form 
piers.  For  interior  partitions,  4-in.  to  8-in.  walls  are  sufficient. 

The  blocks  are  made  by  three  styles  of  hydraulic  press  —  (1)  a 
portable  hand  press,  which  will  turn  out  (with  five  men)  400 
blocks  per  day;  (2)  a  power  press,  operated  by  electric  motor  or 
gasoline  engine  (to  be  used  in  connection  with  a  power  concrete 
mixer),  which  will  turn  out  (with  six  men)  1000  blocks  per  day; 
(3)  a  heavy  duty  machine,  operated  by  a  10-horse-power  engine 
(serving  both  for  the  press  and  the  concrete  mixer),  which  gives 
35  tons  pressure  to  each  block  and  turns  out  (with  eight  men) 


BUILDING  CONSTRUCTION  33 

1500  blocks  per  day.  Two  masons  and  a  helper  can  lay  400 
blocks  in  a  day. 

F.  E.  Kidder  reports  that  with  hand  mixing  and  a  hand  press, 
operated  by  five  men,  the  cost  of  making  blocks  8f  in.  by  23}  in. 
for  a  square  yard  of  10-in.  wall  (12  blocks  required),  the  concrete 
being  1  part  cement  to  6  parts  sand  and  gravel,  was  0.78  sack  of 
cement  (4  sacks  to  the  barrel),  4  cu.  ft.  of  gravel,  and  the  labor 
of  one  man  for  1.25  hour.  Reckoning  labor  at  $2  per  10  hours, 
gravel  at  75c.  per  load  of  1.25  yd.,  and  cement  at  $2.50  per  bbl., 
the  cost  per  square  yard  was  84c.  Allowing  48c.  per  square  yard 
for  laying  and  mortar,  and  lOc.  per  square  yard  for  carting,  the 
total  cost  per  square  yard  of  wall  erected  was  $1.43  =  15  7-9c. 
per  square  foot.  As  compared  with  walls  of  common  brick,  faced 
with  pressed  brick,  this  is  a  great  saving.  It  is  indeed  consider- 
ably lower  than  what  the  most  ordinary  brick  masonry  can  be 
laid  for,  since  a  10-in.  wall  of  this  concrete  construction  will 
satisfactorily  take  the  place  of  a  13-in.  or  17-in.  brick  wall.  It 
should  be  noted  also  that  Mr.  Kidder's  test  was  made  with  hand 
machines,  and  naturally  the  cost  of  the  blocks  would  be  reduced 
by  mechanical  mixing  and  power  press.  The  figures  refer,  more- 
over, to  so-called  " faced"  blocks,  in  the  manufacture  of  which 
0.25  in.  of  the  concrete  is  scraped  off  the  face,  which  is  then 
surfaced  smoothly  with  1 :  2  cement.  When  taken  from  the  press 
the  blocks  are  stacked  up  for  10  days,  and  are  kept  moist  by 
spray  from  overhead  sprinklers. 

This  appears  to  be  a  form  of  building  construction  which  is 
well  worthy  of  attention,  not  only  because  of  its  economy,  but 
also  because  of  its  advantages  in  other  respects.  The  hollow 
walls,  divided  by  partitions,  make  the  building  cool  in  summer 
and  warm  in  winter,  while  the  spaces  can  be  utilized  for  heating 
and  ventilating  flues,  electric  wires,  plumbing  pipes,  etc. 


CORRUGATED  IRON  BUILDINGS 

BY  W.  R.  INGALLS 

(September  19,  1903) 

Corrugated  sheet  iron  is  one  of  the  most  useful  and,  under 
many  conditions,  one  of  the  cheapest  of  materials  for  buildings 
for  metallurgical  purposes,  particularly  for  roofs.  The  linear 
rigidity  imparted  to  light  sheets  by  the  process  of  corrugation 
makes  them  self-supporting  and  gives  strength  to  the  light  and 
comparatively  inexpensive  framing  on  which  they  may  be  used. 
The  framing  may  be  either  of  timber  or  steel.  The  essential 
parts  of  such  a  building  are  merely  the  posts,  girts,  wall  plates, 
trusses,  and  purlins,  on  the  last  of  which  the  corrugated  sheets 
are  laid  directly. 

Corrugated  sheet  iron  is  sold  either  as  galvanized  or  painted. 
The  former  is  the  more  expensive,  but  also  the  more  durable;  it 
is,  however,  quite  unsuitable  for  buildings  intended  to  contain 
furnaces  which  will  develop  sulphurous  fumes,  since  the  latter 
will  quickly  corrode  the  zinc  with  which  the  iron  is  coated,  and 
the  galvanic  action  set  up  between  the  remaining  zinc  and  the 
uncoated  iron  hastens  the  destruction  of  the  latter.  With  any 
kind  of  corrugated  sheet  iron  the  durability  depends  upon  the 
thoroughness  with  which  the  iron  is  protected.  On  this  account 
galvanized  sheets  are  sometimes  painted,  though  commonly  used 
without  any  other  protection  than  is  afforded  by  the  coating  of 
zinc.  Ordinary  corrugated  iron  receives  one  coat  of  paint  at  the 
rolling-mill,  the  paint  usually  employed  being  red  oxide  of  iron, 
thoroughly  ground  in  pure  linseed  oil,  with  enough  drier  mixed 
in  to  give  it  proper  drying  qualities.  This  first  coat  of  paint  3 
applied  by  machine,  and  is  likely  to  be  imperfect,  wherefore  tha 
sheets  should  be  painted  again  after  putting  them  on  the  building. 
For  this  purpose  other  paints  than  ferric  oxide  may  be  used 
advantageously,  such,  for  example,  as  graphite  or  silica-graphite. 
Corrugated  iron  sheets  may  be  obtained  from  the  rolling-mills 

34 


BUILDING  CONSTRUCTION  35 

painted  with  graphite  or  other  special  paints  at  an  additional 
cost  over  the  ordinary  sheets. 

Corrugated  sheet  iron  is  sold  either  by  the  pound  or  by  the 
''square"  of  100  sq.  ft.  In  calculating  the  latter  the  full  width 
and  length  of  the  sheets,  after  being  corrugated,  is  counted;  no 
allowance  is  made  for  end  or  side  laps.  The  approximate  weight 
in  pounds  per  100  sq.  ft.  of  corrugated  sheet  iron,  with  2J-in. 
corrugations,  of  various  thickness,  per  United  States  standard 
gage,  is  given  in  the  following  table: 

Gage,   No 28        27        26        24        22        20        18        16 

Painted,  Ib 70        76        82      110      140      166      220      275 

Galvanized,    Ib 87        93        99      127      157      183      237      292 

Standard  corrugated  iron  sheets,  with  2J-in.  corrugations,  are 
26  in.  wide,  and  will  lay  24  in.  wide,  with  a  side  lap  of  one  corru- 
gation. They  are  made  in  lengths  of  6,  7,  8,  9,  and  10  ft.  When 
sufficient  time  (usually  about  two  weeks)  is  given,  sheets  may  be 
rolled  to  special  intermediate  lengths,  but  if  sheets  have  to  be 
cut,  the  next  larger  length  is  charged  for;  thus,  an  order  for 
sheets  8  ft.  8  in.  long  would  be  charged  at  the  price  of  9-ft.  sheets. 
The  dimensions  of  sheets  of  standard  sizes  and  the  surface  that 
they  will  lay  is  given  in  the  following  table: 

Length,  ft 6    7    8  9  10 

Width,  in. 26  26  26  26  26 

Area,  sq.  ft 13  15£  17}  19i  21f 

Will  lay,  sq.  ft 12  14  16  18"  20 

The  figures  in  the  last  line  of  the  above  table  make  no  allow- 
ance for  end  laps,  and  in  estimating  must  be  diminished  by  the 
proportion  of  the  latter  to  the  length  of  the  sheets.  On  siding  a 
1-in.  or  2-in.  end  lap  is  sufficient,  but  on  roofing  it  varies  from, 
3  to  6  in.,  according  to  the  pitch  of  the  roof. 

In  laying  corrugated  iron  a  nail  should  be  put  in  at  every 
other  corrugation,  at  the  end  laps  and  about  every  6  in.  on  the 
side  laps,  nailing  through  the  ridges  of  the  corrugations  and  not 
through  the  furrows.  Nails  of  1-in.,  IJ-in.  and  2^-in.  lengths  are 
employed;  certain  patent  barbed  roofing  nails,  which  cannot 
work  out,  the  necks  being  barbed,  may  be  recommended.  In 
order  to  make  a  perfectly  tight  roof  the  sheets  should  have  a 
side  lap  of  one  and  a  half  corrugations,  whereby  water  would 
have  to  flood  up  under  two  full  corrugations  before  it  could  do 


36 


METALLURGICAL  MILL  CONSTRUCTION 


any  damage.  A  side  lap  of  two  corrugations  is  sometimes  used, 
but  is  no  better  than  a  lap  of  one  and  a  half.  In  sidings  a  lap  of 
one  corrugation  is  amply  sufficient. 

•  When  a  corrugated  iron  roof  is  to  be  laid  on  boards  nailed  to 
the  rafters,  it  is  advisable  to  lay  waterproof  paper  between  the 
iron  and  the  boards,  especially  in  buildings  where  steam  or  vapor 
comes  in  contact  with  the  roof.  The  paper  makes  the  building 
warmer  and  prevents  dripping  from  the  roof.  Good  waterproof 
paper  may  be  bought  at  20c.  to  25c.  per  100  sq.  ft. 

If  there  are  valleys  in  the  roof,  form  a  lining  from  plain  sheet 
iron  or  steel,  painted  on  both  sides,  from  18  to  24  in.  wide,  fit  it 
in. the  valley,  and  cut  corrugated  iron  to  correspond,  lapping  the 
latter  from  4  to  6  in.  over  the  valley  lining.  To  cover  the  comb 
of  the  roof,  metal  ridge  caps,  usually  in  lengths  of  8  ft.,  may  be 
obtained.  These  are  made  with  corrugations  to  fit  into  those  of 
the  roof  sheets,  thus  making  a  tight  and  well-finished  roof.  Metal 
corner-boards,  casings  for  window  sills,  and  louver  slats  are  also 
articles  of  regular  manufacture. 

The  distance  between  purlins  that  is  to  be  spanned  by  corru- 
gated iron  sheets  laid  directly  upon  them  is  determined  by  the 
transverse  strength  of  the  iron  and  the  load  to  be  sustained.  In 
the  parts  of  the  United  States  where  the  snowfall  is  likely  to  be 
heavy,  roofs  are  generally  made  capable  of  supporting  30  to  50  lb. 
per  square  foot,  allowing  for  snow  and  wind  pressure.  According 
to  William  Kent  (" Mechanical  Engineer's  Pocket-Book,"  p.  181), 
it  was  found  by  actual  trial  that  No.  20  corrugated  iron,  spanning 
6-;ft.,  began  to  give  a  permanent  deflection  under  a  load  of  30  lb. 
per  square  foot,  and  collapsed  under  60  lb.  The  distance  between 
centers  of  purlins  should  not,  therefore,  exceed  6  ft.  for  a  load  of 
30  lb.  per  square  foot,  and  preferably  should  be  less  than  that. 
Jones  &  Laughlin  give  the  following  safe  loads,  in  pounds  per 
square  foot,  for  standard  corrugated  sheets  supported  by  purlins 
3,  4,  5,  6,  and  7  ft.  apart: 


B.  W.  G. 

3  FT. 

4  FT. 

5  FT. 

6  FT. 

7  FT. 

No  16 

135 

76 

49 

34 

25 

No.  18 

102 

57 

37 

25 

18 

No.  20  

73 

41 

26 

18 

14 

No.  22  

58 

33 

21 

14 

10 

No.  24  

46 

26 

16 

11 

8 

No.  26 

38 

21 

13 

9 

5 

BUILDING  CONSTRUCTION  37 

The  above  figures  give  a  factor  of  safety  of  4.  Corrugated 
iron  sheets  are  the  stiffer  the  larger  the  corrugations.  The 
transverse  strength  of  corrugated  iron  is  computed  by  the  for- 
mula, W  =  99/900TBD  -  L,  in  which  W  is  the  breaking 
weight  in  pounds,  T  the  thickness  of  the  sheet  in  inches,  B  the 
breadth  of  the  sheet' in  inches,  D  the  depth  6f  the  corrugations  in 
inches,  and  L  the  unsupported  length  in  inches. 

The  cost  of  an  iron  and  steel  building  depends  chiefly  upon 
the  total  weight  of  the  material  required  in  its  sbnstrucfton. 
This  will  correspond  approximately  to' the  area -of  ground  cbvered, 
and  the  latter  is  a  convenient  basis  for  rough  estimates.  Gen- 
erally speaking,  the  complete  cost  of  a  one-story  iron1  building, 
such  as  would  be  suitable  for  a  furnace  shed,  storage  house,  £tc., 
is  40c.  to  60c.  per  square  foot  of  ground  covered.  A  building 
309  by  42  ft.,  weighing  10.5  Ib.  per  square -foot,  cost  44.65c.  per 
square  foot.  Other  buildings,  weighing  15  Ib.  per  square  'foot, 
cost  57.5c.  and  60c.  These  costs  did  not  include  the  footings  -or 
pavements  of  the  floors.  They  figure  out  to  4c.  to  4.25c.  per 
pound,  and  were  done  at  a  time  when  steel  was  high  (1900  and 
1901). 


IRON  AND  STEEL  BUILDINGS 

(January  14,  1904) 

According  to  Professor  Ketchum,  in  his  treatise  on  the  design 
of  steel  mill  buildings,  the  minimum  size  of  angle  bars  to  be 
employed  in  the  construction  of  such  buildings  should  be  2  by 
2  by  0.25  in.,  and  the  minimum  thickness  of  plates  0.25  in.  for 
both  permanent  and  temporary  structures.  Wherever  the  metal 
is  to  be  subjected  to  corrosive  gases,  as  in  train  sheds  and  smelter 
buildings,  the  ordinary  allowable  stresses  should  be  decreased 
20  to  25  per  cent.,  and  the  minimum  thickness  of  metal  increased 
25  per  cent.,  unless  the  metal  be  fully  protected  by  an  acid-proof 
.coating.  The  best  paints  at  present  in  use  do  little  more  than 
delay  and  retard  corrosion.  The  minimum  thickness  of  corru- 
gated sheet  steel  for  roof  covering  should  be  No.  20  gage  and  for 
the  sides  of  buildings  No.  22  gage,  but  where  there  is  certain  to 
be  no  danger  of  corrosion,  Nos.  22  and  24  may  be  used  for  the 
roof  and  sides,  respectively. 

He  states  also  that  the  cost  of  making  details  for  the  head- 
works  of  mines  is  from  $4  to  $6  per  ton;  for  churches  and  court- 
house roofs,  having  hips  and  valleys,  from  $6  to  $8  per  ton;  for 
ordinary  mill  buildings  from  $2  to  $4  per  ton;  the  details  for  all 
the  work  done  in  a  year  by  a  large  structural  concern  were  con- 
tracted at  $2.06  per  ton,  which  price  netted  the  contractor  a  fair 
profit.  The  details  for  the  buildings  for  the  Basin  &  Bay  State 
smelting  plant  at  Basin,  Montana,  containing  270  tons  of  steel, 
cost  $2  per  ton. 


38 


NOTES  ON  TIMBER 

(June  16,  1904,  and  July  29,  1905) 

The  following  rules  for  the  inspection  of  yellow  pine,  adopted 
at  the  recent  meetings  of  the  Georgia  Interstate  Saw  Mill  Asso- 
ciation and  the  South  Carolina  Lumber  Association,  are  of  in- 
terest to  constructing  engineers:  All  lumber  must  be  sound,  well 
manufactured,  full  to  size  and  saw-butted;  free  from  unsound, 
loose,  and  hollow  knots,  worm-  and  knot-holes,  through  shakes  or 
round  shakes  that  show  on  the  surface;  square  edge  unless  other- 
wise specified.  A  " through  shake"  is  defined  to  be  through, 
or  connected  from  side  to  side,  edge  to  edge,  or  side  to  edge. 
In  the  measurement  of  dressed  lumber,  the  width  and  thickness 
before  dressing  must  be  taken;  less  than  one  inch  is  to  be 
measured  as  one  inch. 

Loren  E.  Hunt,  Government  engineer  in  charge  of  timber 
testing  for  the  Pacific  coast,  in  a  paper  read  at  the  Engineering 
Congress,  at  Portland,  Oregon,  June  29  to  July  3,  1905,  referred 
to  the  first  systematic  effort  to  test  the  mechanical  properties  of 
timber,  by  the  late  J.  B.  Johnson,  at  Washington  University, 
St.  Louis,  in  1891,  and  continued  by  giving  in  detail  the  present 
methods  in  use  by  the  Bureau  of  Forestry.  He  presented  data 
showing  comparative  results,  from  large  timbers  of  all  grades,  to 
small  selected  specimens,  and  from  red  (Douglas)  fir  to  Western 
hemlock.  The  large  timber  was  found  to  develop  a  modulus  of 
rupture  of  from  50  to  90  per  cent,  of  that  shown  by  the  small 
specimens,  depending  upon  the  dimensions  and  conditions  of 
specimens.  Western  hemlock  was  found  to  develop  somewhat 
over  80  per  cent,  as  much  strength  and  elasticity  as  the  red  fir. 
In  the  discussion,  results  were  given  of  some  recent  tests  of 
Alaska  spruce,  made  at  the  University  of  Washington,  Seattle, 
in  which  the  results,  from  7-  by  8-in.  specimens,  cut  from  small 
trees  and  full  of  knots,  were  less  (though  not  to  any  great  extent) 
than  those  obtained  from  Western  hemlock  and  the  poorer 
qualities  of  fir. 


DESIGN  OF  TIMBER  TRUSSES 

(September  26,  1903 

The  overwhelming  importance  of  steel  in  modern  structural 
work  detracts  from  the  engineering  interest  in  timber  work,  but 
the  latter  is  nevertheless  still  largely  used,  and  doubtless  will  be 
so  long  as  it  is,  for  many  purposes,  cheaper  than  steel.  Steel 
construction  has  the  great  advantage  over  timber  in  the  fact 
that  the  strength  of  the  material  can  be  far  more  accurately 
determined.  Steel  and  iron  are  likely  to  be  fairly  uniform;  the 
reverse  is  the  case  with  timber.  It  is  now  generally  recognized 
that  the  data  as  to  the  strength  of  timber  determined  from  small 
pieces,  as  given  in  the  older  hand-books  and  text  books,  are  un- 
safe. Professor  Lanza  has  concluded,  from  the  results  of  his 
numerous  tests  on  large,  commercial  timbers  at  the  Massachusetts 
Institute  of  Technology,  that  the  breaking  strength  of  long-leaf 
Southern  pine  should  not  be  figured  at  more  than  5000  lb.;  the 
Division  of  Forestry  of  the  Department  of  Agriculture  has  adopted 
4650  lb.  as  the  basis  of  its  calculations.  These  new  data  have 
not  upset  old  calculations,  except  in  so  far  as  they  have  made  it 
clear  that,  in  assuming  maximum  fiber  stress  of  1200  lb.,  the 
factor  of  safety  is  only  about  4,  instead  of  6  or  more,  as  used  to 
be  reckoned. 

In  the  ordinary  timber  truss,  wherein  the  necessary  sizes  of 
the  various  members  have  been  carefully  computed,  the  weakest 
points  are  likely  to  be  the  joints.  Special  care  should  be  given, 
therefore,  to  the  making  of  the  joints  as  strong  as  the  other  parts. 
This  is  emphasized  in  the  valuable  little  book  on  the  "  Design  of 
Simple  Roof  Trusses"  recently  published  by  Prof.  Malverd  A. 
Howe,  which  may  profitably  be  studied  by  the  designers  of  such 
trusses.  Another  valuable  reference  is  a  paper  by  Major  G.  K. 
Scott-Moncrieff  on  tests  of  full-sized  timber  trusses,  published  in 
the  Journal  of  the  Royal  Institute  of  British  Architects,  Jan.  14, 
1899.  These  tests  were  made  largely  to  determine  the  accuracy 
of  Tredgold's  rules  as  to  the  proportions  and  construction  of 

40 


BUILDING  CONSTRUCTION  41 

timber  trusses,  on  which  British  practice  has  been  extensively 
based,  and  also  to  show  the  actual  behavior  under  a  breaking 
strain  of  more  rationally  designed  trusses.  Various  of  the  latter 
failed,  not  by  the  yielding  of  any  member,  but  by  the  shearing 
of  the  end  of  the  tie  beam  because  of  the  defective  character  of 
the  joint.  The  tendency  to  lateral  deflection  was  observed  to  a 
marked  extent,  demonstrating  the  importance  of  a  well-designed 
lateral. bracing  between  trusses,  which  function  in  a  roof  is  to  a 
considerable  degree  fulfilled  by  the  purlins.  The  importance  of 
providing  means  for  tightening  the  various  joints  at  will  was 
also  remarked. 

The  various  conditions  for  a  well-designed  roof  truss  of  wood 
are  met  by  the  selection  of  a  suitable  and  economical  form;  the 
proper  concentration  of  strains  of  triangles  and  parallelograms  of 
forces,  avoiding  the  introduction  of  bending  moments;  the  accu- 
rate determination  of  the  sizes  of  the  various  members,  using  a 
safe  fiber  stress  as  determined  by  the  recent  investigations  of 
different  timbers,  making  due  allowance  for  the  condition  of  the 
latter,  and  the  intelligent  arrangement  of  the  joints.  In  the 
last  connection,  little  reliance  is  to  be  placed  on  the  expensive 
and  complicated  methods  of  mortising  and  tenoning  prescribed 
in  the  older  methods  of  carpentry,  but  rather  on  the  proper  use 
of  iron  straps,  bolts  and  washers,  while  cast-iron  parts  in  the 
form  of  brace  and  rafter  shoes,  king-heads  and  queen-heads,  etc., 
are  often  to  be  recommended. 


SAW-TOOTHED  ROOF  CONSTRUCTION 

(February  3,  1906) 

The  new  erecting  and  machine  shop  of  the  Pittsburg  &  Lake 
Erie  Railroad  at  McKees  Rocks,  Pa.,  has  a  modified  form  of 
saw-toothed  roof  that  presents  some  novel  methods  of  dealing 
with  ordinary  conditions.  The  steel  work  for  this  building  was 
designed  by  Albert  Lucius,  of  New  York,  and  was  fabricated 
and  erected  by  the  McClintic-Marshall  Construction  Co.,  Pittsburg, 
Pa. 

The  steel  skeleton  is  enclosed  by  18-in.  curtain  walls  of  brick; 
both  steel  and  brick  work  are  carried  on  concrete  foundations. 
The  building  is  533  ft.  long  and  is  divided  transversely  into  three 
spans  and  longitudinally  into  bays  of  22  ft.  The  erecting  shop 
occupies  the  higher  portion  on  the  south  side  of  the  building 
(a  span  of  68  ft.  9  in.)  and  extends  the  full  length,  while  the 
machine  shop  occupies  the  entire  north  side;  it  is  approximately 
100  ft.  wide  (in  two  spans)  and  also  extends  the  full  length. 

One  electric  crane  of  120  tons  capacity  and  one  of  10  tons 
capacity,  each  traveling  on  a  separate  runway,  serve  the  erecting 
shop;  their  respective  spans  are  65  ft.  and  62  ft.  center  to  center 
of  crane  rails;  and  the  machine  shop  is  covered  by  two  7J-ton 
cranes,  one  in  each  span.  The  span  of  these  cranes  is  46  ft.  3  in. 
All  cranes  run  the  entire  length  of  the  building. 

The  arrangement  of  the  building  is  shown  in  the  accompanying 
cross-section,  Fig.  1.  In  the  plane  of  the  roof  trusses  is  a  system 
of  longitudinal  bracing  which,  in  connection  with  similar  vertical 
bracing  between  the  columns,  is  designed  to  take  the  stresses 
arising  from  the  load  and  motion  of  the  crane.  The  columns 
which  support  the  roof  are  separate  from  the  crane  columns,  but 
both  are  composed  of  channels  and  plates,  of  box  section;  the 
crane  runways  are  of  the  usual  plate-girder  construction,  except 
that  lateral  stiffness  is  provided  to  resist  the  thrust  of  the  crane 
when  the  trolley  is  suddenly  stopped.  The  girders  for  the  120-ton 
crane  are  5  ft.  deep. 

42 


BUILDING  CONSTRUCTION 


43 


U- 


METALLURGICAL  MILL  CONSTRUCTION 


Details  of  the  roof  are  shown  in  the  cross-section,  Fig.  1,  and 
also  in  the  detail  Qf  the  saw-toothed  construction,  Fig.  2.  This 
is  used  above  the  machine-shop  section  of  the  building.  The 
details  of  the  saw-tooth  construction  show  a  cross-section  through 
the  windows  at  the  quarter  points  of  the  machine-shop  roof. 

The  roof  itself  consists 
of  a  base  of  If -in.  tongued 
and  grooved  boards,  upon 
both  erecting  and  machine- 
shop  sections,  and  upon 
this  is  laid  the  roofing  felt. 
Inside  drainage  is  used 
to  eliminate  the  possibility 
of  water  backing  up,  due  to 
freezing  of  conductor  pipes. 
The  conductor  pipes  are 
5  in.  in  diameter,  on  the 
erecting-shop  section,  and 
lead  from  the  flashing 
boxes  to  the  longitudinal 
discharge  pipes,  of  which 
there  is  one  8  in.  in  diame- 
ter, carried  along  under 
each  side  of  the  roof  and 
supported  by  the  steel 
work,  as  shown  in  Fig.  1. 
For  the  machine  shop, 
4-in.  conductors  lead  from 


FIG.  2.  —  Detail  of  Saw-tooth  Construc- 
tion. 


the  flashing  boxes  to  5-in.  vertical  discharge  pipes,  which  are  ar- 
ranged alongside  of  alternate  columns  of  the  middle  row,  ex- 
tending through  the  shop.  There  are  12  low  points  in  the  roof 
construction  to  provide  drainage. 

The  saw-tooth  windows  are  arranged  to  be  operated  in  sections 
from  the  floor  of  the  shop  by  hand- wheels;  the  mechanism  for 
this  purpose  is  shown  in  Fig  2.  This  gives  ample  ventilation, 
and  obviates  the  necessity  for  any  further  provision  for  that 
purpose. 


NOTES  ON  ROOFS  AND  ROOF  COVERINGS 

BY  W.  R.  INGALLS 

(September  5,  1903) 

There  is  a  great  variety  of  roofing  material,  but  for  mining  and 
metallurgical  works  it  is  necessary  to  obtain  a  roof  which  will  be 
reasonably  cheap  and  at  the  same  time  fairly  durable.  The 
element  of  first  cost  excludes  roofing  with  slate  and  the  more 
expensive  metals,  which  for  general  architectural  work  are 
doubtless  the  best;  moreover,  the  acid  fumes  given  off  in  many 
metallurgical  works  would  be  very  destructive  to  certain  metals, 
such  as  sheet  zinc  and  copper.  With  these  limitations,  the  ques- 
tion of  roofing  is  often  a  serious  problem,  unless  it  be  possible  to 
design  the  buildings  so  that  the  roofs  will  have  such  a  slight 
pitch  as  1 : 24,  commonly  called  a  flat  roof,  in  which  case  the 
problem  is  simplified  by  putting  on  a  covering  of  tar  and  gravel, 
which  makes  not  only  one  of  the  best  kinds  of  roof  in  respect  to 
durability,  low  cost  of  maintenance  and  safety  against  fire,  but 
also  is  one  of  the  cheapest;  in  fact,  it  is  probably  the  cheapest  of 
first-class  roofs.  The  limitation  to  the  use  of  tar  and  gravel, 
however,  is  the  inability  to  apply  it  properly  to  roofs  of  steep 
pitch,  the  tar  having  a  tendency  to  melt  and  run  off  in  the  hot 
weather  of  summer,  and  unfortunately  the  exigencies  of  metal- 
lurgical construction  demand  often  a  roof  of  30  deg.  to  45  deg. 
pitch.  It  is  the  most  serious  question,  therefore,  to  determine 
what  may  best  be  put  on  such  a  roof. 

It  may  be  assumed  that  such  a  roof  will  be  trussed,  the  trusses 
bearing  the  purlins  to  support  the  roof  sheathing.  The  roof 
sheathing  may  consist  of  metal  nailed  directly  to  the  purlins;  or 
it  may  be  some  flexible  material  laid  on  1-in.  boards,  the  latter 
being  nailed  to  the  purlins  so  that  they  will  be  parallel  with  the 
pitch  of  the  roof,  or  else  nailed  to  jack  rafters  which  are  themselves 
carried  by  the  purlins;  of  these  two  methods,  the  former  is  the 
cheaper;  the  stiffness  of  a  yellow  pine  board  one  inch  thick  is 

45 


46  METALLURGICAL  MILL  CONSTRUCTION 

such  that,  when  nailed  to  purlins  spaced  36  in.  apart,  center  to 
center,  the  roof  will  be  good  for  a  snow  and  wind  load  of  40  Ib. 
per  square  foot,  which  is  generally  assumed  in  designing  in  the 
northern  part  of  the  United  States. 

Roofs  prepared  in  the  manner  described  above  may  be  covered 
with  corrugated  iron,  usually  of  No.  22  gage,  laid  directly  on 
the  purlins.  If  the  purlins  be  boarded  over,  the  boarding  may 
be  covered  with  corrugated  iron  of  a  lighter  gage,  say  No.  27, 
or  with  shingles,  or  with  some  kind  of  so-called  ready  roofing. 
The  latter  material  is  usually  a  woolen  felt  saturated  with  coal 
tar  and  rolled  out  in  two  or  three  layers,  with  a  layer  of  coal  tar 
composition  between  the  layers  of  felt.  If  the  material  consists 
of  two  layers  of  felt,  it  is  referred  to  as  two-ply;  if  of  three  layers, 
it  is  referred  to  as  three-ply.  Similar  ready  roofing  is  made  of 
felt  saturated  with  asphaltum,  or  with  paraffine,  or  some  other 
analogous  waterproof  substance. 

The  ready  roofing  is  put  up  in  rolls  of  convenient  size.  In 
laying  on  the  roof,  a  roll  is  unwound  parallel  with  the  eaves,  and 
after  nailing  to  the  boards  another  roll  is  unwound  and  laid  so  as 
to  overlap  the  first  by  about  two  inches.  The  lap  is  cemented 
by  means  of  a  composition  of  pitch,  and  is  securely  tacked  down. 
After  the  entire  roof  is  covered,  the  tack  heads  at  least,  and 
sometimes  the  whole  roof,  is  coated  with  composition,  which  may 
finally  be  sprinkled  with  sand  or  fine  gravel.  The  sand  or  gravel 
greatly  increases  the  durability  of  the  roof.  A  roof  laid  with 
good  three-ply  material,  the  laps  well  cemented  together  and 
tacked  down,  and  the  surface  covered  with  coal  tar,  using  about 
1.5  gals,  per  100  sq.  ft.,  which  is  about  as  much  as  can  be  made 
to  remain  on  a  roof  of  steep  pitch,  and  finally  thoroughly  sanded, 
makes  about  as  good  a  roof  as  is  required  for  ordinary  purposes. 
Its  cost  should  not  be  more  than  $2  to  $2.50  per  square,  com- 
pleted. 

A  shingle  roof  is  durable,  but  is  somewhat  more  expensive  than 
a  roof  covered  with  prepared  felt.  At  present  prices  corrugated 
iron  is  one  of  the  most  expensive  of  the  cheaper  roofing  materials, 
and  also  it  is  one  of  the  least  durable,  its  first  cost  being  increased 
by  the  necessity  for  repainting  the  sheets  as  they  are  received 
from  the  factory,  and  the  cost  of  maintenance  being  considerable 
because  of  the  further  paintings  that  are  frequently  required  if 
the  life  of  the  material  is  to  be  preserved  at  all. 


BUILDING  CONSTRUCTION  47 

The  approximate  cost  of  various  roofing  per  100  sq.  ft.  is 
summarized,  as  follows: 

Boards  and  tarred  felt : 

110  ft.  of  1-in.  board  at  $20 $2.20 

Carpenters'  labor,  nails,  etc 50 

Three-ply  ready  roofing,  in  place 2.50 

Total $5.20 

Boards  and  shingles,  laid  4  in.  to  weather: 

110  ft.  1-in.  board,  at  $20 $2.20 

900  shingles,  at  $3  per  M 2.70 

Roofing  paper 25 

Labor,  nails,  etc 1.91 

Total.. $7.06 

Corrugated  iron  No.  22  gage,  laid  directly  on  the  purlins: 

160  Ib.  of  corrugated  iron  sheets,  at  3c $4.80 

Labor,  nails,  etc 1.00 

Painting  214  sq.  ft 1.41 

Total $7.21 

Corrugated  iron,  No.  27  gage,  laid  on  boards: 

110  ft.  of  1-in.  board,  at  $20 $2.20 

89  Ib.  of  corrugated  iron  sheets,  at  3.6c 3.20 

Roofing  paper 25 

Labor,  nails,  etc 1.50 

Painting  214  sq.  ft 1.41 

Total $8.56 

In  the  above  estimates  the  price  of  corrugated  iron  has  been 
reckoned  at  2.4c.  per  Ib.  for  No/  22  gage  and  3c.  per  Ib.  for 
No.  27  gage  in  car-load  lots  f.  o.  b.  Pittsburg,  Pa.,  or  Youngs- 
town,  O.  It  has  been  reckoned  that  the  under  side  of  the  sheets 
is  to  be  painted  with  silica-graphite  before  the  sheets  are  put  on, 
and  that  the  entire  upper  surface  is  to  be  painted  with  the  same. 
In  the  case  of  the  corrugated  iron  laid  on  boards,  and  also  in 
the  case  of  the  shingle  roof,  it  is  assumed  that  a  sheet  of  good 
waterproof  paper  will  be  interposed  between  the  boards  and  the 
iron  or  the  shingles,  respectively.  In  computing  the  cost  of  the 
boards  allowance  of  10  per  cent,  is  made  for  waste.  It  is  assumed 
that  the  boards  will  be  laid  on  purlins  spaced  36  in.  apart  center 
to  center.  In  the  case  of  the  corrugated  iron  of  No.  22  gage, 


48  METALLURGICAL  MILL  CONSTRUCTION 

the  purlins  may  be  spaced  a  little  further  apart,  and  there  will 
be  a  small  saving  on  that  account,  but  this  will  not  be  of  great 
significance. 

Tar  and  gravel  covering  is  generally  put  on  a  roof  of  1-in. 
boards,  laid  on  rafters,  or  else  on  3-in.  plank,  grooved  and  splined 
(or  tongued  and  grooved),  laid  directly  on  the  main  roof  girders. 
The  latter  makes  the  better  roof,  and  is  prescribed  by  the  insur- 
ance companies  for  standard  mill  construction.  In  that  form  of 
construction  the  roof  girders  will  be  heavy  beams,  spaced  some- 
thing like  8  to  10  ft.  apart;  if  the  beams  be  spaced  10  ft.  apart, 
they  should  be  not  less  than  8  by  10  in.  for  a  16-ft.  span.  If 
the  spacing  be  more  than  10  ft.,  which  is  unusual,  a  heavier  plank 
than  3-in.  is  required.  A  3-in.  plank  on  10-ft.  span  is  good  for 
a  net  load  of  40  Ib.  per  sq.  ft.  within  the  limit  of  deflection  that 
can  be  allowed. 

In  making  a  tar  and  gravel  roof,  several  layers  of  saturated 
woolen  felt  are  first  put  on.  The  surface  of  the  roof  is  finally 
covered  with  coal-tar  pitch,  and  a  sufficient  body  of  well  screened 
gravel  to  give  the  desired  surface.  If  four  layers  of  felt  are  put 
on,  the  roof  is  referred  to  as  four-ply;  if  five  layers,  it  is  referred 
to  as  five-ply. 

There  are  various  methods  of  putting  on  the  felt  and  pitch. 
One  method  for  a  five-ply  roof  is  to  put  on  a  first  layer  of  heavy 
dry  felt,  with  2-in.  lap.  The  other  four  layers  are  then  put  on 
in  courses  parallel  with  the  eaves,  each  layer  lapping  the  one 
below  by  27  in.,  so  that  the  roof  will  be  five  layers  in  thickness 
over  all  its  parts.  Each  layer  is  well  mopped  with  hot  pitch  for 
a  distance  of  9  in.  from  the  edge.  The  felt  is  secured  to  the 
roof  by  3-dwt.  nails  with  tin  disks,  driven  in  rows  10  ft.  apart 
and  12  in.  apart  in  the  rows.  The  entire  surface  of  felt  is  finally 
coated  with  straight  run  coal-tar  pitch  and  covered  immediately 
with  a  sufficient  body  of  well  screened  gravel. 

Another  method  is  to  put  on  three  layers  of  saturated  felt, 
as  described  above,  each  layer  lapping  24  in.;  then  cover  with 
pitch  and  apply  one  or  two  layers  of  felt  separately  in  hot  pitch. 
This  makes  a  very  good  and  durable  roof. 

A  third  method,  which  is  the  one  most  commonly  employed, 
at  least  in  the  Eastern  States,  consists  in  putting  on  three  layers 
of  felt  over  the  whole  surface,  lapping  each  layer  3  in.,  and  then 
mopping  thoroughly  with  pitch,  using  not  less  than  3  gal.  per 


BUILDING  CONSTRUCTION  49 

square.  Two  more  layers  are  then  laid  in  hot  pitch,  so  that  the 
roof  will  have  five  plies  of  felt  over  all  its  parts.  The  last  layer 
is  secured  to  the  roof  at  the  laps  by  3-dwt.  nails  with  tin  disks 
spaced  30  in.  apart.  The  surface  of  the  roof  is  finally  covered 
with  hot  pitch,  using  not  less  than  8  gal.  per  square. 

In  all  methods  the  roof  is  finished  against  chimneys,  party 
walls,  scuttles,  etc.,  by  turning  up  the  felt  4  in.  against  the  wall, 
and  over  this  laying  an  8-in.  strip  of  felt  with  half  its  width  on 
the  roof.  The  upper  edge  of  the  strip  and  the  several  layers  of 
felt  are  fastened  to  the  wall  by  laths  or  battens  securely  nailed, 
and  the  strip  of  felt  is  pressed  into  an  angle  of  the  wall  and 
cemented  to  the  roof  with  hot  pitch,  the  lower  edge  of  the  strip 
being  nailed  to  the  roof  every  4  or  5  in.  Especial  care  must  be 
taken  in  fitting  around  the  angles  of  chimneys  and  skylights. 

The  felt  for  a  tar  and  gravel  roof  should  be  made  of  the  best 
woolen  rag  fiber,  and  should  weigh  about  15  Ib.  per  100  sq.  ft. 
of  roof.  The  felt  comes  in  rolls,  containing  108  sq.  ft.  The 
coating  composition  should  be  straight  run  coal-tar  pitch;  it 
should  be  the  residuum  from  a  distillation  at  comparatively  low 
temperature,  distillation  at  too  high  a  temperature  being  liable 
to  drive  off  some  of  the  valuable  constituents.  The  pitch  will 
weigh  about  10£  Ib.  per  gal.,  and  not  less  than  11  gal.  should  be 
used.  The  gravel  should  be  clean  and  free  from  loam,  and 
should  be  as  dry  as  possible.  If  the  roof  is  laid  in  cold  weather 
the  gravel  must  be  applied  hot.  The  gravel  is  used  in  size  varying 
from  that  of  a  pea  to  about  £-in.  diameter.  Sufficient  gravel  is 
required  to  cover  the  roof  thoroughly,  about  four  bushels  per 
square  being  used  generally  in  laying  a  good  roof.  The  cost  of 
putting  on  a  first-class  five-ply  tar  and  gravel  roof  is  approximately 
as  follows: 

75  Ibs.  of  felt,  at  3c $2.25 

11  gals,  of  pitch,  at  lie 1.21 

4  bushels  of  gravel,  at  20c 80 

Nails,  tin  disks,  etc 10 

Labor 1.00 

Total $5.36 

The  cost  will,  of  course,  vary  according  to  the  prices  for 
various  materials,  especially  the  felt,  which  is  worth  generally 
2c.  to  2fc.  f.  o.  b.  factory. 


50  METALLURGICAL  MILL  CONSTRUCTION 

Tar  and  gravel  roofs  are  frequently  put  on  for  less  cost  than 
$5  per  square;  even  for  as  little  as  $3  per  square;  these  cheaper 
roofs  are  generally  of  only  four-ply,  however,  and  the  material 
used  is  neither  first-class  in  quality,  nor  in  sufficient  quantity. 
The  felt  will  be  of  light  weight,  and  the  quantity  of  pitch  employed 
will  not  be  what  it  should  be. 

The  putting  on  of  tar  and  gravel  roofing  should  be  entrusted 
only  to  experienced  roofers.  Specifications  for  such  roofs  should 
prescribe  the  number  of  layers  of  felt  to  be  used,  its  weight  per 
square,  and  the  quantity  of  pitch  and  gravel.  A  good  method 
in  cases  where  a  large  amount  of  roofing  is  to  be  done  is  to  buy 
the  material  directly  from  the  dealers  and  contract  the  labor. 
The  builder  may  then  be  sure  what  quality  and  quantity  of 
material  is  being  used. 


PROTECTION  OF  IRON  AND  STEEL 

(September  5,  1903) 

Maximilian  Toch  in  the  Journal  of  the  American  Chemical 
Society  for  July,  1903,  discusses  the  question  of  the  permanent 
protection  of  iron  and  steel,  which  is  one  of  the  greatest  impor- 
tance, in  view  of  the  large  extent  to  which  steel  is  employed  in 
modern  construction.  Both  exposed  and  imbedded  iron  are 
subject  to  progressive  oxidation  under  certain  conditions.  Manu- 
facturers of  paints  have  long  endeavored  to  devise  a  coating  of 
material  which  will  prevent  corrosion  and  oxidation.  The  success 
of  such  coatings  depends  chiefly  upon  the  skill  of  the  workman 
and  their  proper  application.  A  good  paint  improperly  applied 
is  relatively  as  poor  as  a  paint  of  less  merit.  Red  lead,  for  exam- 
ple, is  condemned  as  often  as  commended;  it  is  probable  that 
those  who  have  commended  it  have  had  it  properly  applied  by 
skilful  workmen  under  favorable  conditions,  and  then  have  had 
it  covered  by  better  paint. 

It  is  a  blunder  to  apply  a  corrosive  oxide  to  a  material  that 
will  corrode.  If  the  paint  itself  be  a  carrier  of  oxygen  and  the 
iron  or  steel  be  subjected  to  the  action  of  alternate  dampness  or 
dryness  or  of  air  charged  with  carbon  dioxide,  progressive  oxida- 
tion is  sure  to  take  place  and  the  tensile  strength  of  the  metal  to 
be  materially  reduced.  Such  conditions  may  readily  occur  when 
a  beam  is  placed  in  a  porous  wall.  If  a  clean,  pure  cement  con- 
crete is  packed  hard  against  an  iron  or  steel  surface,  little  or  no 
oxidation  can  take  place,  especially  if  free  lime  has  been  liberated 
in  the  setting  of  the  cement,  but  violent  oxidation  may  take 
place  if  cinder  concrete  containing  iron  oxides,  other  metallic 
oxides,  free  chlorine,  or  any  trace  of  a  sulphide  be  used.  Pieces 
of  anchor  chains  imbedded  in  concrete  more  than  200  years  have 
been  found  in  Spain  in  a  state  of  perfect  preservation.  Large 
quantities  of  metal  unearthed  in  Italy  and  Greece,  extremely  old, 
imbedded  in  cement  or  concrete  are  wonderfully  well  preserved. 
These  observations  caused  Mr.  Toch  to  experiment  with  portland 

51 


52  METALLURGICAL  MILL  CONSTRUCTION 

cement  for  the  protection  of  iron  and  steel.    The  result  of  his 
experiments  led  him  to  conclude  as  follows: 

1.  If  a  proper  cement  paint  be  applied  to  a  surface  which 
has  begun  to  oxidize,  further  oxidation  will  be  arrested. 

2.  If  the  cement  used  be  very  fine  and  free  from  iron,  calcium 
sulphate,  and  sulphides  of  low  specific  gravity,  it  will  quickly  set 
on  the  surface  and  eventually  become  thoroughly  fixed  upon  the 
metal  so  that  rain  will  not  wash  it  off. 

3.  When  thoroughly  applied,  even  to  three  coats,  the  concrete 
may  be  painted  with  alkali  proof  and  adherent  paint,  affording 
absolute  protection  to  iron,  so  that  moisture,  carbon  dioxide,  or 
factory  fumes  will  not  penetrate.    . 

4.  Cement  paste  for  application  to  iron  or  steel  must  be  made 
with  pure  water,  and  the  mixture  must  be  stirred  at  least  fifteen 
minutes  to  admit  of  the  liberation  of  the  lime. 

5.  Free  lime  on  the  surface  of  the  cement  coating  is  quickly 
carbonated,  and  then  has  no  injurious  action  upon  linseed  oil 
paint,  which  may,  under  such  conditions,  be  applied  and  become 
extremely  efficacious. 

It  is  reasonable  to  believe  that  structural  metal  work  coated 
with  a  layer  of  cement  paint  and  further  protected  by  a  layer  of 
hydrocarbon  insulating  paint,  when  imbedded  in  masonry,  will 
be  perfectly  immune  to  oxidation  and  probably  will  last  for  all 
time.  A  similar  coating  will  afford  sufficient  protection  to  pipes 
and  conduits  placed  in  the  ground  and  subjected  to  various 
influences,  such  as  of  moist  gases,  electric  currents,  acid  and 
alkaline  liquids.  Pure  port  land  cement  mixed  with  water  cannot 
be  used  as  a  metal  wash  because  it  will  not  always  set  and  is  apt 
to  crack  when  it  does;  hence  it  must  be  diluted  and  care  must  be 
exercised  so  as  not  to  impair  the  strength  of  the  cement.  Voids 
can  be  prevented  by  careful  brushing,  and  for  certain  structural 
work,  where  application  by  the  brush  is  inapplicable,  spraying  is 
effective,  but  the  cement  must  then  be  applied  in  several  layers. 

The  waterproofing  of  brick  walls  from  the  outside  as  a  pro- 
tection against  penetrating  rain  or  dampness  is  an  important 
consideration.  A  newly  laid  brick  contains  as  much  as  8  oz.  of 
water,  and  its  power  to  adhere  to  the  mortar  increases  with  the 
quantity  of  water  it  contains.  If  a  linseed  oil  paint  be  applied 
to  a  newly  erected  and  wet  wall  it  quickly  peels  off  and  ruins  the 
wall  for  the  further  application  of  paint.  However,  if  a  proper 


BUILDING  CONSTRUCTION  53 

cement  mixture  be  applied  to  such  a  wall  in  the  form  of  a  paint 
or  wash  it  not  only  adheres  perfectly,  but  forms  an  excellent 
base  for  the  application  of  a  good  linseed  oil  paint.  Painting  the 
outside  wall  of  a  building  in  this  way  is  something  of  a  protection 
to  the  iron  and  steel  used  in  construction,  since  it  prevents  to  a 
large  extent  the  access  of  carbon  dioxide,  moisture,  and  gases. 


PROTECTION  OF  STEEL  FROM  CORROSION 

BY  CHARLES  L.  NORTON 

(February  18,  1904) 

Previous  tests,  carried  out  on  perfectly  clean  steel,  have  been 
repeated  on  specimens  in  all  degrees  of  initial  corrosion,  doubt 
having  existed  as  to  whether  the  results  found  with  clean  steel 
would  apply  to  rusty  or  dirty  steel.  The  specimens  were  imbedded 
in  concrete  mixed  in  the  proportion  of  1:2.5:5  to  1:3:6.  The 
cements  used  were  Alpha,  Lehigh,  and  Alsen.  Care  was  taken 
in  selecting  the  sand  and  stone,  the  latter  being  of  such  size  as  to 
pass  a  1-in.  mesh. 

The  results  of  the  tests,  which  were  carried  out  under  various 
conditions,  lead  to  the  conclusion  that  structural  steel,  if  encased 
in  a  sound  sheet  of  good  concrete,  is  safe  from  corrosion  for  a 
very  long  period  —  longer  than  the  changes  in  our  cities  will 
allow  any  building  to  remain.  It  is  necessary,  however,  to  be 
sure  that  the  steel  is  properly  encased  in  the  concrete,  and, 
because  of  the  difficulty  in  getting  sound  work,  many  engineers 
will  not  use  concrete.  This  is  especially  true  of  cinder  concrete, 
in  which  the  porous  nature  of  the  cinder  has  led  to  much  dry 
concrete,  and  many  voids  and  much  corrosion. 

There  can  be  no  question  that  cinder  concrete  has  rusted 
great  quantities  of  steel,  not  because  of  its  sulphur  content,  the 
danger  from  which  is  a  myth,  but  because  it  was  mixed  too  dry, 
through  the  action  of  the  cinders  in  absorbing  moisture,  and 
therefore  contained  voids;  and,  moreover,  because  the  cinder 
often  contains  oxide  of  iron,  which,  when  not  coated  with  the 
cement  by  thorough  wet-mixing,  causes  rusting  of  the  steel  which 
it  touches.  If  cinder  roncrete  be  mixed  wet  and  mixed  well,  it 
may  be  trusted  as  much  as  stone  concrete,  so  far  as  corrosion  is 
concerned. 


54 


SPECIFICATIONS  FOR  PAINTING  STEEL  STRUCTURAL  WORK 

(October  10,  1903) 

The  painting  specifications  for  the  superstructure  of  the 
Blackwell's  Island  bridge  across  the  East  River  at  New  York, 
contracts  for  which  have  just  been  let,  are  of  general  interest  to 
engineers.  They  are  as  follows: 

All  material  shall  be  received  and  painted  under  cover;  and 
no  painting,  either  at  the  works  or  in  the  field,  shall  be  done  in 
wet  or  freezing  weather.  All  structural  steel  and  iron  before 
leaving  the  shop  must  be  thoroughly  cleaned  of  all  mill  scale, 
dirt,  and  rust,  by  the  use  of  small  hammers,  steel  scrapers,  and 
wire  brushes,  and  of  oil  by  the  use  of  benzine,  and  must  then 
receive  one  coat  of  red  lead  and  boiled  linseed  oil.  These  materials 
must  be  brought  to  the  work  in  their  original  packages  and  mixed 
in  a  revolving  churn  just  before  using,  in  the  proportion  of  33  Ib. 
of  dry  red  lead  to  one  gallon  of  linseed  oil. 

The  red  lead  must  be  strictly  pure,  and  shall  contain  at  least 
80  per  cent,  of  true  red  lead  (of  the  composition  Pb3O4);  the  total 
amount  of  lead  present  shall  not  be  less  than  89  per  cent.,  of 
which  not  more  than  0.1  per  cent,  shall  be  present  as  metallic 
lead.  The  color  shall  be  clean  and  pure  tint.  The  red  lead 
shall  be  of  the  fineness  that,  when  washed  with  water  through  a 
No.  19  silk  bolting-cloth,  no  more  than  1  per  cent,  shall  be  left 
on  the  screen.  The  linseed  oil  shall  be  an  absolutely  pure  boiled 
oil,  containing  no  matters  volatile  at  212  deg.  F.  in  a  current  of 
hydrogen;  it  shall  not  contain  any  rosin  or  manganese.  The  oil 
shall  be  perfectly  clear  on  receipt  and  no  deposit  shall  form  on 
standing,  provided  the  oil  is  kept  at  a  temperature  above  45  deg. 
F.  The  film  left  after  flowing  the  oil  over  the  glass  and  allowing 
it  to  drain  in  a  vertical  position  must  be  dry  to  the  touch  after 
24  hours.  All  finished  surfaces  shall  be  coated  with  white  lead 
and  tallow  before  being  shipped  from  the  shop. 

After  the  structure  is  in  place  all  mud  and  dirt  that  may 
have  accumulated  during  the  erection  must  be  removed,  and  all 

56 


56  METALLURGICAL  MILL  CONSTRUCTION 

abrasions  in  the  first  coat  of  paint  must  be  thoroughly  brushed 
with  a  stiff  wire  brush  and  such  places  "  touched  up,"  and  all 
bolt  heads  and  location  marks  thoroughly  painted  with  the  paint, 
as  described,  and  then  all  the  steel  and  iron  work  shall  be  thor- 
oughly and  evenly  painted  with  an  additional  coat  of  red  lead 
and  boiled  linseed  oil,  of  the  quality  stated,  mixed  in  a  revolving 
churn  in  the  proportion  of  33  Ib.  of  red  lead  to  one  gallon  of  oil, 
with  the  addition  of  J  Ib.  of  best  lampblack  (ground  in  oil)  to 
every  99  Ib.  of  red  lead  used.  The  second  field  coat  shall  consist 
of  red  lead  and  boiled  linseed  oil,  without  lampblack. 


STAMP  MILL  CONSTRUCTION 

(February  23,  1905) 

In  replying  to  the  discussion  of  his  paper  on  "Mill  Construc- 
tion, Milling,  and  Amalgamation/'  I.  Roskelly  stated  (Journal  of 
the  Chemical,  Metallurgical,  and  Mining  Society  of  South  Africa) 
that  many  points  of  agreement  among  mill-men  had  been  brought 
out,  among  which  should  be  emphasized: 

1.  More  mill  space  than  is  usually  allowed  should  be  provided. 

2.  Concentrates  should  be  recrushed. 

3.  Special  precautions  should  be  taken  for  reducing  vibration. 

4.  Solid  wooden  guides  have  yet  to  be  improved  upon. 

5.  Extra  mechanical  contrivances  for  facilitating  work  should 
be  supplied. 

6.  Special  precautions  should  be  taken  if  cyanide  is  used. 

7.  Outside  amalgamation  is  to  be  preferred. 

8.  A  thoroughly  adequate  crusher  plant  should  be  provided. 

9.  Ten  stamps  on  a  shaft  is  not  an  improvement. 

10.  The  new  Blanton  cam  is  an  improvement  on  keyed  cams. 

The  so-called  improved  feeders  do  not,  in  Mr.  Roskelly 's 
opinion,  justify  discarding  the  Challenge  feeder,  but  probably  an 
improvement  will  be  made  in  that,  so  that  the  brake-wheel  and 
three  pawls  can  be  done  away  with. 

Most  contributors  to  the  discussion  advocated  either  the 
sparing  use  of  cyanide  or  its  total  abolition.  Mr.  Roskelly  con- 
siders, however,  that  it  merely  cleans  and  brightens  the  plates 
and  has  never  found  that  it  hardens  amalgam,  nor  does  it  dissolve 
amalgam  to  any  appreciable  extent. 

Outside  amalgamation  pure  and  simple  has  proved  itself  to 
be  as  good  as,  if  not  better  than,  any  other  method,  and  it  is 
the  method  which  reduces  losses  and  risks  of  all  kinds  to  the 
minimum.  With  inside  amalgamation  the  mill-man  is  working 
more  or  less  in  the  dark. 

57 


DESIGN  OF  ORE-BINS  AND  COAL-POCKETS 

(May  5,  1904) 

This  is  a  subject  that  is  apt  to  be  troublesome  to  the  metal- 
lurgical engineer,  because  of  the  lack  of  data.  The  gross  weight 
that  must  be  carried  is  easily  estimated,  but  the  manner  in  which 
it  will  exert  its  pressure,  not  so  easily.  Recourse  has  been  made 
to  the  formulas  for  retaining  walls  and  other  indirect  methods. 
S.  A.  Jamieson,  elevator  engineer,  of  Montreal,  Can.,  in  a  paper 
on  "  Grain  Pressures  in  Deep  Bins,"  read  before  the  Canadian 
Society  of  Civil  Engineers,  December,  1903,  has  thrown  some 
light  on  this  subject.  Although  his  experiments  referred  espe- 
cially to  the  behavior  of  cereal  grains,  he  also  showed  that  dry 
sand  acted  in  a  quite  similar  way,  and  it  is  not  improbable  that 
the  same  general  rules  apply  to  heavier  mineral  particles  under 
the  same  conditions  of  dry  ness,  etc. 

Mr.  Jamieson's  paper  is  too  long  and  intricate  to  be  sum- 
marized satisfactorily  in  a  brief  note.  The  nature  of  his  conclu- 
sions, however,  is  indicated  in  the  statement  that,  in  a  deep  bin, 
only  a  small  proportion  of  the  weight  of  the  material  is  carried 
on  the  bottom,  the  major  portion  —  depending  upon  the  depth 
of  the  bin  —  being  exerted  against  the  sides,  where  it  is  resolved 
into  vertical  pressure  by  friction.  The  proportion  of  the  total 
weight  of  grain  in  a  bin  that  is  carried  by  the  walls  and  on  the 
bottom,  and  therefore  the  intensity  of  both  the  vertical  and 
lateral  pressures,  is  entirely  dependent  upon  the  following  factors: 
(1)  Coefficient  of  friction  between  the  granular  material  and  the 
bin  walls;  (2)  ratio  of  the  breadth  or  diameter  of  the  bin  to  the 
depth;  (3)  ratio  of  the  horizontal  area  or  weight  of  the  column 
to  the  area  of  the  bin  walls;  (4)  angle  of  repose  of  the  granular 
material,  or  the  ratio  of  lateral  to  vertical  pressure. 


58 


NEW  CHANGING-HOUSE  AT  CLIFFS  SHAFT  MINE  l 
BY  JOHN  S.  MENNIE 

(September  12,  1903) 

On  the  night  of  Dec.  1,  1901,  the  changing-house  at  the 
Cliffs  Shaft  mine  was  totally  destroyed  by  fire,  causing  quite  a 
financial  loss  not  only  to  the  Cleveland-Cliffs  Iron  Company  on 
the  building,  but  also  to  its  employees  on  their  clothing.  The 
losses  on  buildings  of  this  description,  when  built  of  wood,  would 
indicate  that  they  are  extra  hazardous,  and  in  fact  the  insurance 
rates  are  almost  prohibitory.  In  considering  the  erection  of  a 
new  building  it  was  thought  that  it  would  be  cheaper  in  the  end 
to  build  it  of  brick,  which,  while  not  absolutely  fireproof,  would 
be  practically  so.  The  other  essential  requirements  were  an  easy 
method  of  keeping  the  building  clean  and  the  best  possible 
arrangements  for  the  comfort  and  cleanliness  of  the  occupants. 

The  building  as  erected  is  30  ft.  4  in.  in  outside  dimensions 
and  11  ft.  from  the  top  of  the  floor  to  the  under  side  of  trusses. 
The  foundation  walls  up  to  the  floor  line  are  built  of  common 
rubble  stone,  laid  up  in  cement.  The  exterior  walls  above  the 
floor  line  are  of  common  brick  laid  up  in  lime  mortar,  and  are 
10  in.  in  thickness,  consisting  of  two  4-in.  courses  of  brick  with  a 
2-in.  air  space  to  prevent  sweating  of  walls.  The  two  courses  of 
brick  are  tied  together  every  fifth  course  with  clipped  headers. 
Where  the  trusses  rest  on  the  walls  piers  are  formed  by  building 
an  extra  course  of  brick  on  the  outside.  Three  division  walls 
run  across  the  building;  they  are  solid,  8  in.  thick,  and  are  carried 
up  to  the  roof  boards  as  fire  walls. 

The  roof  is  carried  on  light  trusses  of  6-  by  6-in.  timber,  spaced 
about  8  ft.  centers.  On  these  are  laid  2-in.  matched  and  dressed 
common  pine,  face  down;  strips  1  by  2  in.  in  size  are  then  nailed 
on  across  this  planking,  spaced  2  ft.  centers  and  then  covered 

1  Abstract  from  Proceedings  of  Lake  Superior  Mining  Institute,  August, 
1903. 

59. 


60 


METALLURGICAL  MILL  CONSTRUCTION 


with  1-in.  common  hemlock  shiplap,  making  a  1-in.  air  space  in 
the  roof.  The  roof  covering  is  two-ply  rubberoid  roofing.  The 
exterior  woodwork  is  painted  two  coats  of  reddish  brown  paint, 
the  interior  woodwork  two  coats  light  drab  paint,  and  the  interior 
brick  walls  were  given  one  coat  of  white  cold  water  paint. 

The  floors  throughout  are  of  concrete  and  all  are  graded  to 
the  center  of  the  rooms  where  connection  is  made  through  gratings 
to  a  6-in.  tile  sewer-pipe.  These  pipes  are  then  carried  under  the 
floor  to  the  outside  of  the  foundation  walls  and  empty  into  a 
box  drain.  The  floor  under  the  shower  baths  is  graded  to  the 
wall  to  a  drain  of  sewer-pipe  split  in  halves,  and  these  are  con- 
nected to  the  main  drain. 


FIG.  3.  —  Cross-section. 


FIG.  4.  —  East  Elevation. 


The  entrance  to  the  building  is  by  two  doors,  one  at  each 
end  of  what  is  termed  the  change-room.  This  room  is  28  by  54  ft. 
in  size.  Against  the  walls  of  this  room  are  set  up  126  lockers 
12  by  12  in.  by  5  ft.  high,  for  street  clothes.  They  are  made  of 
expanded  metal,  and  being  each  used  by  a  night  and  a  day  man, 
they  accommodate  252  men. 

In  the  center  of  the  room  are  two  drying  racks  for  mine 
clothes.  These  are  made  from  1-in.  iron  pipe  and  fittings  and 
have  four  bars  each.  Over  each  of  these  racks  is  a  large  venti- 
lating hood  made  of  galvanized  iron  on  IJ-in.  angle-iron  frames; 
these  rise  into  three  16-in.  pipes  which  are  carried  through  the 
roof  and  capped  with  16-in.  "Star"  ventilators.  Stationary 
benches  of  2-in.  plank  on  iron  standards  extend  the  full  length 
on  each  side  of  the  room  between  the  lockers  and  the  drying  racks. 

From  the  north  end  of  this  room  entrance  is  had  through 
two  doors  to  the  wash-room,  which  is  28  by  46  ft.  in  size.  Run- 
ning lengthwise  of  this  room  are  three  wash-troughs.  These  are 


BUILDING  CONSTRUCTION 


61 


62  METALLURGICAL  MILL  CONSTRUCTION 

made  of  J-in.  iron  bent  to  a  semicircle  and  are  set  up  on  iron 
standards  built  into  the  concrete  floor.  Hot  and  cold  water  is 
brought  into  the  building  through  separate  pipes  in  a  tile-pipe 
conduit  under  the  floor  and  is  distributed  in  two  separate  pipes 
to  each  trough  and  extended  the  full  length  with  upright  con- 
nections to  faucets  about  5  ft.  apart.  On  these  pipes  and  the 
edge  of  the  trough  rest  individual  enameled  iron  wash-basins. 
Each  man  draws  clean  water  into  his  basin  tempered  for  heat  to 
suit  himself,  and  after  washing  empties  it  into  the  trough,  when 
it  immediately  runs  off  to  the  drain.  This  system  of  wash- 
troughs  and  basins  was  in  use  at  the  Champion  Iron  Company's 
mine  at  Beacon,  and  seemed  to  be  so  clean  and  admirable  in  every 
way  that  it  was  adopted  in  this  building. 

Against  one  of  the  walls  are  arranged  ten  shower-bath  stalls 
about  4  ft.  square  in  size  and  7  ft.  high.  The  frames  of  these 
are  of  1-in.  angle  iron  and  are  covered  with  corrugated  iron  to 
within  about  18  in.  from  the  floor.  The  door  opening  is  provided 
with  a  drop  curtain  of  linoleum.  Each  stall  is  fitted  with  a  spray 
shower-bath  fixture  with  mixing  chamber,  and  supplied  with  hot 
and  cold  water. 

In  the  north  wall  of  this  room  are  three  doors,  the  center  one 
opening  into  a  janitor's  closet  for  keeping  brooms,  hose,  etc., 
the  other  two  into  rooms  each  11  ft.  by  11  ft.  6  in.  in  size.  Both 
rooms  have  large  closets.  One  of  these  rooms  is  used  by  the 
shift-bosses  as  a  change-room  and  office,  the  other  as  an  emergency 
hospital,  and  is  fitted  up  with  operating  table,  stretcher,  and 
surgical  appliances.  The  closet  has  shelves  and  is  supplied  with 
such  medical  supplies  as  might  be  needed  in  case  of  accident. 
This  room  has  a  wide  door  as  an  outside  entrance. 

Returning  to  the  change-room  there  are  two  doors  opening 
from  its  south  end  into  a  room  20  by  28  ft.  in  size,  used  as  a 
dining-room.  This  room  was  put  on  as  an  experiment.  It  is 
fitted  with  two  long  tables  and  benches.  Being  a  separate  room 
and  separately  heated  it  is  much  more  comfortable  to  sit  in  than 
the  change-room.  Its  use  also  tends  to  keep  the  change-room 
cleaner.  As  the  room  is  now  used  to  its  capacity  it  would  seem 
to  be  advisable  to  extend  this  feature  in  any  similar  building 
hereafter  erected,  so  as  to  accommodate  all  the  men  who  may 
use  the  building.  The  building  is  heated  by  the  Webster  vacuum 
system,  using  exhaust  steam.  The  steam  is  brought  into  the 


BUILDING  CONSTRUCTION  63 

building  under  the  floor  through  iron  pipes  in  a  tile-pipe  conduit 
and  distributed  to  the  different  coils  of  pipe.  These  coils  are 
placed  under  the  lockers,  benches,  clothes-racks  and  wash-troughs. 
The  other  rooms  are  heated  by  wall  coils. 

The  entire  cost  of  the  building  was  $6604. 

Commenting  on  the  building  after  being  in  use,  I  would  say 
that  the  lockers  for  street  clothes  are  rather  small  and  that  the 
12  by  16  in.  locker  of  same  make  should  be  used.  They  would 
be  large  enough  in  cases  where  the  one  shift  is  up  and  changed 
before  the  other  shift  begins  to  change.  The  amount  of  wash- 
trough  room  is  more  than  is  required,  and  might  be  cut  down 
one-third  for  the  number  of  men  arranged  for  in  the  building. 
The  danger  of  fire  is  reduced  to  a  minimum,  and  in  fact  is  prac- 
tically confined  to  the  clothes  in  the  change-room.  The  doors  in 
this  room  leading  to  other  rooms  have  been  tin-clad,  and  we 
think,  if  a  fire  should  occur  in  the  clothes,  that  no  part  of  the 
building  would  be  damaged  to  any  material  extent. 


DUST-PROOF  PARTITIONS 

(October  3,  1903) 

In  a  dry-crushing  mill,  there  is  sometimes  great  difficulty  in 
constructing  partitions  which  will  absolutely  confine  the  dust. 
No  matter  how  carefully  matched  boards  are  put  up,  or  paper 
sheathing  is  put  on,  some  dust  will  work  through. 

A  good  and  cheap  method  of  preventing  this  is  to  make  the 
partition  of  ordinary  boards  and  seal  the  joints  with  strips  of 
muslin,  glued  on.  Cut  the  muslin  into  strips  about  4  in.  wide. 
Apply  glue  to  the  boards  for  about  1  in.  on  each  side  of  the  joint. 
Lay  on  the  strip  of  muslin  and  with  a  case-knife  (or  similar  thin, 
blunt  tool)  crease  it  into  the  joint.  Be  sure  that  the  muslin  is 
thoroughly  glued  to  the  boards.  The  crease  of  the  muslin  inside 
of  the  joint  allows  for  the  opening  of  the  latter  as  the  boards 
shrink,  and  the  crack  remains  sealed  by  a  medium  which  will 
prevent  any  dust  from  passing  through. 

This  method  is  due  to  the  late  Henry  A.  Vezin,  to  whom  the 
mining  and  metallurgical  profession  owes  many  useful  inventions. 
His  method  of  making  dust-proof  partitions  has  been  adopted 
in  many  dry-crushing  mills,  and  it  has  proved  thoroughly 
serviceable. 


64 


PART  III 
ORE-CRUSHING  MACHINERY 


CAPACITY  OF  BLAKE  CRUSHERS 

BY  W.  R.  INGALLS 

(October  31,  1903) 

The  capacity  of  a  crusher  of  the  Blake  type  depends  chiefly 
upon  the  width  of  the  jaw,  the  speed  at  which  it  is  driven,  the 
size  to  which  the  ore  or  stone  is  crushed,  and  the  character  of 
the  ore  or  stone.  As  in  the  case  of  rolls  and  other  crushing 
machines,  the  capacity  is  more  accurately  stated  in  terms  of 
volume,  i.e.,  cubic  yards  or  cubic  feet,  than  in  terms  of  weight, 
because,  all  other  things  being  equal,  a  crusher  will  deliver  more 
tons  of  a  heavy  ore  than  of  a  light  ore.  With  respect  to  the 
character  of  the  material  to  be  crushed,  hard  ore  or  stone  that 
breaks  with  a  snap  will  go  through  faster  than  less  brittle  stuff; 
one  of  the  hardest  materials  to  crush  is  soft,  talcose,  tough  stuff, 
that  mashes  and  is  broken  only  with  difficulty.  With  some  such 
kinds  of  material  it  is  almost  impossible  to  get  it  through  the 
crusher  at  all. 

There  are  practically  no  published  data  as  to  the  capacity  of 
crushers  on  different  kinds  of  ore,  nor  of  the  power  required. 
The  data  given  in  the  catalogues  of  various  manufacturers  are 
quite  unreliable,  varying  greatly.  As  a  matter  of  interest  I 
have  summarized  the  statements  with  respect  to  the  9-  by  15-in 
machine  given  in  the  catalogues  of  eight  prominent  manufacturers;. 
The  following  table  gives  the  total  weight  of  the  machine  manu- 
factured by  each,  the  speed  at  which  it  is  recommended  to  drive, 
the  estimated  horse-power  required,  and  the  tons  of  product 
made  per  hour  in  crushing  to  about  1.5-in.  size.  Many  of  these 
manufacturers  state  that  the  figures  quoted  are  only  approximate, 
but  few  express  any  recognition  of  the  fact  that  output  should 
be  stated  in  cubic  feet  and  not  in  tons,  and  few  specify  as  to  the 
character  of  ore  upon  which  their  figures  are  based.  The  presump- 
tion is  that  quartzose  ore  is  especially  referred  to.  .  .  .  . 

67 


68  METALLURGICAL  MILL  CONSTRUCTION 

DATA  OF  9-IN.  BY  15-IN.  BLAKE  CRUSHERS 


WEIGHT,  LBS. 

SPEED,  R.  P.  M  . 

H.  P.  REQUIRED 

TONS  PRODUCT 

PER  HOUR 

No.  1     

16,000 

250 

10 

15.Q 

No.  2  

15,000 

250 

12 

5.56 

No  3 

16900 

250 

10 

10.5 

No  4 

15,750 

300 

12 

5.5c 

No  5                  

14,000 

275 

15 

ll.O/ 

No.  6a  
No.  7  

16,500 
16,500 

275 
250 

12 
10 

16.0<f 
8.0e 

No  8 

16000 

250 

10 

10.5/ 

(a)  The  crusher  made  by  this  manufacturer  is  10  in.  by  16  in. 

(6)  This  manufacturer  rates  the  capacity  as  10  tons  per  hour  in  crushing 
to  2.5-in.  size,  8  tons  in  crushing  to  2-in.  size,  and  5.5  tons  in  crushing  to 
1.5-in.  size. 

(c)  This  manufacturer  gives  the  same  figures  as  the  one  quoted  above, 
with  the  additional  statement  that  in  crushing  to  1-in.  size  the  capacity  is 
only  4  tons  per  hour. 

(d)  The  size  of  the  crushed  product  is  not  stated  by  this  manufacturer. 

(e)  This  manufacturer  rates  the  capacity  as  8  tons  per  hour  in  crushing 
to  2-in.  size,  4  tons  in  crushing  to  1-in.  size,  and  2  tons  in  crushing  to  0.5-in. 
size. 

(/)  This  figure  is  for  crushing  to  2-in.  size. 

The  machines  to  which  the  data  here  tabulated  refer  are 
built  by  well-known  and  reputable  firms,  whose  work  has  stood 
the  test  of  years.  It  will  be  observed  that  there  is  very  little 
difference  in  the  quantity  of  material  put  in  any  of  them,  the 
weights  running  in  all  cases  close  to  16,000  Ib.  There  is  a  close 
agreement  in  the  idea  that  the  proper  speed  for  these  machines 
is  250  to  275  revolutions  per  minute,  and  with  a  single  exception 
the  estimate  of  power  required  is  10  to  12  horse-power.  With 
respect  to  the  rated  capacity,  however,  there  is  a  wide  variation, 
this  ranging  from  5.5  tons  per  hour  crushed  to  1.5-in.  size  up  to 
15  tons  per  hour  crushed  to  the  same  size.  It  is  obviously  im- 
possible that  two  equally  well-built  crushers  of  the  same  size 
and  type  should  show  such  differences  as  0.66  horse-power  and 
2  horse-power  per  ton  of  stone  broken  (in  all  well-built  crushers 
the  friction  is  about  the  same),  and  the  reporting  of  such  data 
betrays  ignorance  somewhere.  There  is  no  doubt  that  the 
manufacturers  who  report  such  an  hourly  capacity  as  15  tons 
greatly  overestimate  the  actual  efficiency  of  their  machines.  One 


ORE-CRUSHING  MACHINERY  69 

well-known  manufacturer,  who  treats  of  the  subject  more  care- 
fully than  most,  states  that  in  crushing  "ordinary  material/' 
with  the  jaws  of  the  crusher  set  about  2  in.  apart  when  closed, 
from  1.25  to  1.5  horse-power  per  ton  of  material  crushed  is  usually 
required. 

For  practical  purposes  the  assumption  that  a  9-in.  by  15-in. 
Blake  crusher,  run  at  250  revolutions  per  minute,  will  break  to 
1.5-in.  size  about  5  to  7  tons  of  brittle  quartzose  ore  per  hour 
with  the  consumption  of  15  horse-power  is  probably  sufficiently 
safe.  The  actual  duty  will  be  governed  largely  by  the  manner 
in  which  the  crusher  is  fed,  the  proportion  of  fine  ore  in  the  stuff 
crushed,  and  upon  whether  or  not  the  fines  are  screened  out 
before  feeding  to  the  crusher.  However,  it  is  to  be  regretted 
that  there  is  such  a  lack  of  accurate  data  as  to  these  common 
machines,  and  especially  such  a  lack  of  data  as  to  the  comparative 
hardness  and  toughness,  breaking  strength,  friability  and  specific 
gravity  of  various  ores.  Such  data  with  respect  to  the  typical 
ores  would  be  of  great  value  to  the  metallurgist. 


A  CANTILEVER  BATTERY  FRAME 
BY  IRA  C.  Boss 

(March  10,  1904) 

The  invention  of  the  gravity  stamp  has  been  credited  to 
Von  Maltitz  about  the  year  1505,  but  the  first  commercial  use 
of  it  was  made  by  Paul  Gromstetter  in  1519,  when  he  established, 
at  Joachimstahl,  a  process  of  wet  stamping  and  sifting.  Until 
the  nineteenth  century  the  stamp  was  merely  a  square  timber 
(with  the  exception  of  a  few  instances  when  square  iron  was 
used)  with  an  iron  shoe  at  the  bottom.  With  the  discovery  of 
gold  in  California  came  the  introduction  of  this  crude  machine, 
and  rapid  improvements  in  its  construction  soon  followed. 

G.  P.  Stanford  introduced  the  round  iron  stem,  and  Isaac  Fish 
suggested  a  method  of  revolving  it.  Zenos  Wheeler  and  H.  B. 
Angel  together  invented  the  method  of  holding  the  tappet  by 
means  of  a  gib  and  two  cross-keys.  Irving  M.  Scott  designed 
and  constructed  the  first  double-arm  cam.  Zenos  Wheeler  is 
also  credited  with  the  high-box  mortar.  About  this  time  the 
long  battery-blocks  set  on  end  came  into  use,  but  the  originator 
is  not  known.  A  general  perfecting  of  details  still  goes  on  from 
year  to  year. 

In  stamp-mill  design  much  attention  has  lately  been  paid  to 
the  construction  of  the  mortar.  A  vigorous  effort  has  been 
made  to  render  the  quadruple  discharge  popular,  but  it  was 
handicapped  at  the  start  by  faulty  construction  and  impatient 
criticism.  The  low  mortar  with  long  stamp-head  is  being  built 
both  at  Chicago  and  San  Francisco.  The  object  of  building  this 
low  mortar  is  to  make  it  possible  to  guide  the  stem  at  a  much 
lower  point  than  is  generally  practised,  so  as  to  decrease  the 
vibration  of  the  stem  and  diminish  the  progress  of  crystallization. 
The  guides  also  should  be  a  snug  bore,  1-64  part  of  an  inch  on 
the  diameter,  affording  plenty  of  clearance.  This  necessitates  a 
careful  alinement  and  a  steady  back  for  the  guides.  Cast  iron 

70 


ORE-CRUSHING  MACHINERY  71 

will  wear  the  stem  much  less  than  wood.  A  solid  cast-iron  guide 
not  less  than  12  in.  long  will  give  excellent  results. 

Forged-steel  shoes  and  dies  give  good  service,  but  are  more 
expensive  than  the  best  cast  steel  and  wear  no  better.  The 
self-tightening  cam  is  being  largely  used,  as  it  is  easily  and  quickly 
removed.  If  the  battery  frame  is  rigid  there  will  be  less  and  a 
more  even  wear  to  the  stem,  shoe,  and  die,  and  less  power  required 
to  do  the  work.  A  battery  frame  of  steel  is  better  than  one  of 
wood,  if  constructed  so  as  to  have  a  minimum  of  vibration,  which 
will  insure  its  own  life  and  that  of  the  stems,  by  holding  the  guides 
firmly  and  always  in  alinement.  The  enormous  production  of 
steel  and  the  improved  railroad  facilities,  together  with  the 
increase  in  price  of  timber,  have  made  it  possible  in  many  localities 
to  lay  down  steel  as  cheaply  as,  if  not  more  cheaply  than,  timber. 

The  accompanying  drawing  shows  the  wooden  cantilever 
battery  frame  and  ore-bin.  This  is  designed  for  districts  where 
timber  is  plentiful  and  when  time  is  limited. 

A  10-stamp  mill  of  this  design,  of  steel  construction,  has  just 
been  erected  at  Tonopah,  Nevada.  It  has  foundations  and 
battery  frame  for  20  stamps,  but  so  far  only  10  have  been  in- 
stalled. The  battery  and  ore-bin  frames,  the  pan  frame,  and 
building  are  all  made  of  steel,  and  the  foundations  and  floors  are 
concrete.  The  object  was  to  do  away  with  the  future  replacing 
of  timbers,  to  give  guides  and  bearings  rigid  support;  the  cement 
floors  were  put  in  to  prevent  loss  of  quicksilver. 

The  battery  frame  is  a  part  of  the  ore-bin  from  which  it  gets 
its  rigidity.  Two  concrete  walls  30  in.  thick  are  the  foundations 
for  a  series  of  24-in.  I-beams  having  5.5-ft.  centers.  These  beams 
extend  out  so  as  to  take  the  bearings  for  the  cam-shaft.  The 
skeleton  of  the  bin  is  of  10-in.  I-beams  and  the  10-in.  cap-channels 
are  a  support  for  a  hanging  strap,  which  catches  the  base  beam, 
near  the  cam-shaft  bearing,  giving  that  bearing  an  extra  support. 
This  construction  leaves  a  clear  passage  around  the  two  five-stamp 
mortars,  which  are  of  the  double  discharge  and  low  type. 

The  lower  guides  are  placed  so  low  that,  when  the  stamp  is 
at  its  highest  point  with  new  shoe  and  a  new  die,  the  top  of  the 
stamp-head  nearly  touches  the  bottom  of  the  guide.  The  housing 
is  around  the  stamp-head  instead  of  enclosing  the  stem;  also  the 
stamp-head  is  reached  more  handily  in  "backing  off"  the  head. 
The  sides  and  bottom  of  the  ore-bin  are  of  reinforced  concrete, 


72 


METALLURGICAL  MILL  CONSTRUCTION 


arched.     The  ends  of  the  bin  are  concrete  walls,  the  bin  and 
battery  occupy  a  minimum  of  space. 

The  Tonopah  mill  consists  of  ten  1300-lb.  stamps;  the  guides 
are  individual,  of  cast  iron  and  15  in.  long.  The  pulp  is  crushed 
wet,  put  through  a  coarse  screen  and  piped  to  two  5-ft.  Hunt  ing  ton 
mills,  used  as  regrinders.  From  these  mills  it  is  taken  to  a  series 


FIG.  6.  —  Cantilever  Battery  Frame,  Wood  Construction. 

of  continuous  pans  and  settlers.  The  pan  frame  is  steel  and  the 
pans  are  overhead  driven,  doing  away  with  the  noisy  gears  which 
are  usually  placed  in  a  dark  and  inconvenient  pit. 

The  cams,  tappets,  shoes,  and  dies  are  of  chrome  steel.  The 
cams  are  self-tightening,  as  is  also  the  cam-shaft  pulley.  A  unique 
detail  of  the  mill  is  a  contrivance  for  hanging  up  the  stems. 


ORE-CRUSHING  MACHINERY  73 

Cast-iron  fingers  with  adjustable  steel  caps  are  mounted  on  a 
4-in.  shaft;  a  lever  for  each  finger  passes  between  the  stems  and 
projects  in  a  handy  position,  so  that,  by  simply  pulling  down  the 
lever  with  one  hand,  the  tappet  is  lifted  out  of  the  way  of  the 
cam.  Lifting  the  lever  puts  it  at  work  again,  and  it  is  all  done 
from  in  front  of  the  mortar,  where  one  wants  it. 

The  concrete  foundation  under  the  battery  is  6  ft.  deep  and 
7  ft.  wide.  The  proportion  of  cement  and  sand  was  varied. 
The  first  2  ft.  were  mixed,  6  of  sand  to  1  of  cement;  the  second 
2  ft.,  5  of  sand  to  1  of  cement;  the  next  foot,  4  of  sand  to  1  of 
cement,  and  the  last  foot  and  also  the  mortar  block  (which 
stands  up  12  in.)  was  mixed  3  of  sand  to  1  of  cement.  It  was 
built  on  a  good  rock  foundation,  and  the  rock  used  in  the  concrete 
was  firm  and  clean,  the  pieces  being  placed  as  close  to  each  other 
as  possible,  while  allowing  the  wet  cement  and  sand  to  imbed 
each  piece  separately.  The  tamping  of  concrete  is  very  impor- 
tant and  also  the  mixing.  It  should  be  tamped  until  the  water 
is  drawn  to  the  surface.  In  mixing  a  given  amount  of  sand, 
generally  measured  by  filling  barrels  and  leveling  off,  it  should 
be  spread  in  a  layer  4  or  5  inches  thick  on  a  mixing  platform. 
The  measured  quantity  of  cement  should  be  evenly  distributed 
over  this.  The  piles  should  then  be  turned  over  several  times 
until  thoroughly  mixed;  then  it  should  be  wetted  down.  The 
mortar-block  should  be  left  one  inch  low,  and  when  the  mortar  is 
placed  in  position  it  is  set  0.25  in.  low  and  then  grouted  up  with 
cement  and  sand  mixed  in  the  proportions  of  two  to  one.  Then, 
when  the  concrete  is  sufficiently  set  the  mortar  is  raised;  a  sheet 
of  rubber,  0.25  in.  thick,  is  placed  on  top  of  the  mortar-block 
and  all  is  finished.  This  gives  a  block  which  will  last  a  lifetime. 
Sand  for  the  concrete  should  be  perfectly  clean;  and  if  it  is  not, 
it  should  be  washed.  A  very  small  quantity  of  lime  added  to 
concrete  in  the  mixing  will  be  found  to  give  it  additional  strength. 

The  stamps  drop  100  times  per  minute,  and  have  a  capacity 
of  between  five  and  six  tons  per  stamp.  The  mill-building  is  all 
steel  and  galvanized  corrugated  iron  with  plenty  of  windows. 
Power  is  furnished  by  a  120-horse-power  Diesel  oil  engine.  The 
mill  is  lighted  throughout  by  electricity.  All  driving  pulleys 
have  friction  clutches  which  permits  of  any  one  part  being  cut 
out  without  shutting  down.  The  retorting  is  also  done  with  oil 
for  fuel.  Owing  to  the  high  freight  rates  over  the  60  miles  of 


74  METALLURGICAL  MILL  CONSTRUCTION 

desert,  wood  and  coal  were  out  of  the  question.     In  a  quartz-mill 
no  power  is  as  satisfactory  as  steam. 

The  mill  was  contracted  for  by  Harron,  Rickard  &  McCone, 
of  San  Francisco.  It  was  planned  by  M.  P.  Boss  and  constructed 
by  the  writer.  The  plant  is  running  splendidly  and  saving  a 
high  percentage  at  a  low  cost. 


BATTERY  FOUNDATIONS 

BY  H.  E.  WEST 

(June  2,  1904) 

In  the  Engineering  and  Mining  Journal  of  March  10  there 
is  an  article  on  a  novel  type  of  battery  design  under  "Notes 
on  a  Cantilever  Battery  Frame,"  by  Ira  C.  Boss.  There  are  one 
or  two  remarks  in  connection  with  the  building  of  the  concrete 
foundation  that  engaged  my  attention.  In  the  first  place,  it 
would  appear  from  the  description  given  that,  although  the 
efficient  mixing  of  concrete  is  advocated,  yet  apparently  the  wet 
batter  of  cement  and  sand  was  added  to  the  broken  stone  in  situ. 
If  this  is  a  correct  reading,  it  would  not  appear  an  advisable 
departure  from  the  usual  practice.  Again,  it  does  not  appear  to 
me  that  the  " grouting  in"  of  the  mortar,  after  the  concrete  block 
has  set,  is  an  advisable  method;  this  quite  customary  method  in 
machinery-setting  has,  in  the  case  of  mortar-setting,  been  fruitful 
of  trouble,  as  may  be  learned  from  the  setting  of  mortars  and 
anvil-blocks  on  concrete  at  the  Alaska  Treadwell  mines  and 
elsewhere.  A  more  approved  method  is  that  given  in  a  previous 
number  of  the  Engineering  and  Mining  Journal,  where  the  writer 
advocated  the  substitution  of  a  wooden  block,  an  exact  duplicate 
of  the  mortar,  being  accurately  set  on  the  yet  pliable  surface  of 
the  rammed  concrete  with  an  added  surface  made  of  a  stiff  mix- 
ture of  sand  and  cement,  the  block  being  screwed  down  and  leveled 
accurately  in  position  and  afterward  removed. 

With  regard  to  that  very  prevalent  practice  of  inserting  a 
piece  of  i-in.  sheet  rubber,  I  cannot  say  that  I  at  all  see  the  neces- 
sity of  this  or  any  other  material  being  inserted  between  the 
mortar  and  its  block.  It  was  all  very  well,  in  the  days  that  I 
can  well  remember,  when  mortars  were  supplied  rough  from 
the  casting.  But  now,  when  they  are  accurately  surfaced,  and 
the  mortar-block  is  also  a  plane  surface,  it  would  appear  to  me 
that  the  very  object  of  the  concrete  foundation  —  an  absolutely 

75 


76  METALLURGICAL  MILL  CONSTRUCTION 

rigid  base  —  is  to  some  extent  discounted  by  the  resilience  of 
the  rubber  sheet.  As  a  matter  of  fact,  I  should  imagine  after 
some  time  that  the  actual  "cushion"  disappeared,  which  was 
the  case  with  the  older  form  of  tarred  blanket. 

It  would  appear  to  me  that  an  absolutely  rigid  connection 
between  the  plane  surfaces  of  the  mortar  bottom  and  the  block 
would  be  more  correct  in  theory,  and  would  yield  better  results 
in  practice,  than  this  present-day  relic  of  "spring-beams"  and 
"  tarred  blankets,"  the  latter  being  necessary  in  the  times  referred 
to,  when  uneven  surfaces  were  presented  to  each  other.  It 
would  be  interesting  to  ascertain  what  results  have  attended 
the  discarding  of  any  filling  or  joining  material,  such  as 
described. 

Support  is  given  in  this  article  to  another  very  popular  delu- 
sion, namely,  the  mixing  of  a  certain  amount  of  lime  with  cement, 
or  vice  versa.  This  is  usually  advocated  for  purposes  of  econo- 
mizing the  cement,  not  because  it  is  beneficial  to  the  cement. 
Seeing  that  cements  are  so  carefully  compounded,  and  that 
"over-liming"  is  carefully  guarded  against,  if  this  very  indefinite 
statement  regarding  the  strengthening  of  the  concrete  by  the 
addition  of  a  small  amount  of  lime  can  be  substantiated  by  the 
results  of  actual  tests,  it  would  appear  that  the  cement  used 
must  have  been  of  an  inferior  order,  and  that  its  composition 
was  defective;  since,  if  it  were  possible  to  augment  its  strengthen- 
ing properties  in  setting,  in  which  the  time  factor  is  also  impor- 
tant, one  would  imagine  that  this  should  have  been  the  careful 
consideration  of  the  chemist  at  the  manufacturer's  works,  and 
not  have  been  left  to  be  discovered  in  actual  construction. 


BATTERY  FOUNDATIONS 

BY  M.  P.  Boss 

(June  30,  1904) 

The  communication  from  H.  E.  West  in  the  Engineering  and 
Mining  Journal  of  June  2,  under  the  head  of  "  Battery  Founda- 
tions/' touches  so  close  to  myself  that  I  feel  prompted  to  write 
a  few  lines.  Being  the  designer,  in  general  and  in  detail,  as  well 
as  the  co -contractor  for  the  Tonopah  mill  in  question,  my  respon- 
sibility in  the  premises  was  paramount. 

It  is  not  so  much  my  purpose  to  explain  the  details  of  this 
specific  case  —  for  they  may  have  already  been  answered  —  as  it 
is  to  touch  upon  the  principles  involved,  not  for  the  sake  of 
contention,  but  that  my  ideas  may  be  known  and  accepted  for 
what  they  may  be  thought  to  be  worth.  However,  Mr.  West's 
inference  that  the  "wet  batter  of  cement  and  sand  was  added 
to  the  broken  stone  in  situ"  is  an  error.  The  concrete  was 
rammed  down  and  coarse  pieces  of  rock  were  individually  and 
separately  inserted  and  rammed  with  it  —  a  practice  I  have 
always  followed,  and  my  battery  foundations  have  always  been 
thoroughly  successful,  except  that  the  first  (which  was  laid  nearly 
sixteen  years  ago)  was  faulty  from  lack  of  careful  ramming. 

Personally,  I  never  use  lime  in  battery  foundations.  At  the 
mill  in  question  it  was  used  only  in  a  trifling  quantity  —  in  theory, 
I  think,  to  counteract  some  fancied  acidity  of  the  water.  As  to 
grouting  under  a  mortar,  if  it  is  carefully  done  on  fresh  concrete, 
it  will  set  just  as  solidly  as  any  other  way  of  putting  it  in;  but 
again,  personally,  I  am  satisfied  to  lay  it  full  up  and  carefully 
sweep  and  dress  the  surface.  In  the  first  mill  I  put  nothing 
between  the  sole  plate  (which  I  used  then  for  the  only  time)  and 
the  concrete.  In  the  second  mill  I  put  nothing  between  the 
mortar  and  concrete  with  four  of  the  batteries,  but  under  two 
mortars  I  put  rubber. 

I  now  always  put  rubber  under  mortars  for  the  reason  that 

77 


78  METALLURGICAL  MILL  CONSTRUCTION 

the  vibration  of  the  mortar,  however  small,  slightly  disintegrates 
the  surface  of  the  concrete,  especially  if  wet,  and  the  gasket 
entirely  prevents  such  action.  As  to  its  being  a  cushion  to  the 
blow,  that  is  infinitesimal  when  added  to  the  weight  of  the  mortar 
is  the  compression  of  four  bolts  of  2J  in.  in  diameter  —  which  is 
my  standard.  Anvil  blocks  under  mortars  I  have  always  con- 
tended were  illogical,  and  my  own  experience  has  demonstrated 
them  to  be  absolutely  unnecessary.  They  are  objectionable 
because  they  are  put  in  the  form  of  a  pedestal;  if  they  were  flat, 
the  only  objection  to  them  would  be  that  of  unnecessary  cost. 

It  seems  to  be  a  popular  idea,  even  among  engineers,  that  the 
great  strain  on  a  battery  foundation  is  downward  from  the  blow 
of  the  stamp.  Now  a  single  blow  from  the  heaviest  stamp,  when 
spread  over  an  area  of  two  thousand  square  inches  (the  space 
occupied  by  the  bottom  of  the  mortar),  gives  a  very  low  square 
inch  pressure,  so  that  it  is  almost  wholly  vibration  from  repeated 
blows  that  gives  to  us  foundation  problems.  A  mortar  set  upon 
a  pedestal,  even  if  the  pedestal  be  of  solid  iron,  has  little  to  resist 
its  vibration  laterally,  and  from  the  top  heaviness  is  more  trying 
upon  the  concrete  surface  than  where  the  mortar  sets  directly 
upon  the  concrete. 

It  is  gratifying  that  criticisms  are  now  upon  details,  and  not 
the  general  idea  of  concrete  foundations,  since  in  building  the 
first  battery  foundation  of  that  kind  I  had  to  defend  my  idea 
single-handed,  for  I  knew  no  engineer,  mill-builder  or  mill-man 
who  endorsed  solid  foundations  for  stamps. 


STAMP  TAPPETS 

BY  M.  P.  Boss 

(October  13,  1904) 

While  in  general  features  the  stamp-battery  is  essentially 
what  it  was  a  third  of  a  century  ago,  it  has  been  touched  up  and 
refined  in  detail,  and  its  efficiency  and  endurance  greatly  aug- 
mented thereby.  What  seem  trivial  details  to  a  layman  in 
mechanics  aggregate  in  a  machine  so  as  to  affect  very  materially 
its  profit-earning  qualities.  Any  one  looking  at  so  simple  a 
thing  as  a  stamp-battery  of  to-day  can  hardly  realize  that  it  has 
been  the  focus  of  many  thinkers  for  many  years.  Nevertheless, 
the  standard  tappet  as  we  use  it  possesses  no  detail  that  was  not 
common  to  it  many  years  ago.  In  fact,  one  detail  commonly 
applied  on  the  Comstock  upward  of  thirty  years  ago,  and  fully 
appreciated  at  that  time,  is  less  generally  used  to-day,  because 
manufacturers  can  save  a  little  expense  when  it  is  not  exacted. 
I  refer  to  the  counterbore. 

Of  course,  before  the  days  of  steel  tappets  much  care  was 
required  not  to  split  the  tappet,  and  that  was  an  added  incentive 
to  its  employment,  yet  none  will  gainsay  that  heavy  driving  of 
tappet  keys  involves  time  and  wear  and  tear.  With  a  proper 
counterbore  but  a  fraction  of  key  pressure  is  required  that  other- 
wise is  necessary  to  hold  a  tappet  from  slipping.  I  use  the  term 
"proper  counterbore"  advisedly,  for,  while  most  understand  the 
"three  bearing  points"  idea,  few  fully  realize  the  wedge  principle 
involved. 

To  demonstrate  fully  the  two  points  referred  to  I  add  the 
drawings  given  in  Figs.  8  to  11. 

In  Fig.  7  the  line  between  A  and  B  is  at  right  angles  to  the 
center  line  intersecting  the  gib,  and  in  the  course  of  rotation  of 
the  stamp  these  points  are  alternately  struck  by  the  cam  in 
operation.  The  blow  being  struck  at  a  point  outside  of  the 

79 


80 


METALLURGICAL  MILL  CONSTRUCTION 


center  line,  through  the  pressure  strain,  clearly  has  a  tendency 
to  swerve  the  tappet  from  alinement  with  the  stem.  If  the 
tappet  yields  in  the  least  infinitesimal  degree  to  this  tendency,  it 
more  than  returns  when  the  blow  follows  upon  the  opposite  side, 
and  the  tappet  will  work  upward  on  the  stem  at  each  recurring 
change  in  alinement. 

Fig.  8  represents  the  plan  of  a  tappet  without  counterbore. 

As,  necessarily,  a  tappet  must  be 
bored  to  an  easy  fit  upon  the  stem, 
when  key-pressure  is  but  lightly  ap- 
plied against  the  gib,  the  contact  of 
tappet-bore  and  the  stem  is  but  a 
narrow  line,  that  gives  weak  resist- 
ance to  the  disalining  influences 
referred  to.  Not  until  the  key-pres- 
sure against  the  gib  is  made  great 
enough  to  develop  the  elasticity  of 
the  metal  in  the  tappet  sufficiently 
to  enwrap  the  stem  with  a  broad  line 
of  contact  opposite  to  the  gib  can  the 
tappet  resist  the  disalining  influences 
of  the  heavy  blows  of  the  cam. 
Even  a  narrow  counterbore  aids  this 
materially,  as  it  gives  two  parallel 
lines  of  contact  opposite  the  gib,  and 
less  key-pressure  is  required.  This 
is  one  feature  of  the  counterbore. 

Figs.  9  and  10  are  the  plans  of 
tappets  with  counterbore.  For  the  sake  of  clearness  in  showing 
the  lines  of  contact  to  stem,  the  metal  is  shown  cut  away  oppo- 
site the  counterbore,  thus  emphasizing  the  contact  points  or 
lines. 

Fig.  9  represents  a  narrow  counterbore,  and  Fig.  10  a  wide  one. 
To  think  of  the  stem  acting  as  a  wedge  between  the  two  points 
of  contact  when  key-pressure  is  applied  is  impossible  with  No.  9, 
but  conceivable  with  No.  10.  Lines  tangent  to  the  stem  at  points 
of  contact  correspond  to  the  plane  surfaces  of  the  wedge  it  rep- 
resents. So,  if  a  counterbore  extends  120  deg. — one-third  of 
the  circumference  —  every  pound  of  pressure  applied  by  the  key 
is  repeated  at  each  of  the  two  other  points,  whereas  where  there 


TTIJ1 

A  L  B 

I 

I 

FIGS.  8  and  7. 


ORE-CRUSHING  MACHINERY 


81 


is  no  counterbore,  the  key-pressure  is  repeated  only  at  the  one 
point  opposite  the  key.     Thus  it  is  shown  that  a  counterbore 
extending   120  deg.  augments  the 
pressure   upon   the    stem    50    per 
cent.     This  is  aside  from  the  ad- 
vantage of  the  widely  apart   par- 
allel lines  of  contact-resisting  disa- 
linement. 

Extending  the  counterbore  be- 
yond 120  deg.,  the  wedging  ad- 
vantage gains  rapidly,  and  it  is 
not  extravagant  to  say  that  a 
tappet  on  a  1200-lb.  stamp  could 
be  successfully  held  by  a  single 
hard-wood  key,  by  means  of  a 
counterbore  of  say  170  deg.  of 
circumference.  Not  by  any  means 
is  it  to  be  inferred  that  this  ex- 
treme is  desirable,  but  a  counter- 
bore  of  120  deg.  or  140  deg.  is 
economy  in  the  long  run. 

Another  feature  in  a  tappet  is 
to  make  the  key-way  openings 
easily  distinguishable,  the  wide 
from  the  narrow.  Rounding  one 
side,  as  shown  in  Fig.  11,  is  sim- 
ple and  effective.  Still  another 
minor  feature  is  that  the  inner 
sides  of  the  flanges  on  a  tappet 
should  be  more  or  less  flattened,  so  that  they  may  be  struck  by 
a  heavy  hammer,  when  moving  a  tappet,  without  battering  or 
disfiguring  its  flanges. 


FIGS.  11,  10,  and  9. 


HORSE-POWER  FOR  TEN-STAMP  BATTERY ' 

BY  FRANK  E.  SHEPAED 

(April  21,  1904) 

Modern  practice  in  stamp  mills  includes  the  use  of  stamps 
with  weights  varying  from  500  to  1200  Ib.  per  stamp,  and  hight 
of  drop  varying  from  4  to  10  in.  The  diagram  herewith  shows 
the  horse-power  required  for  each  10-stamp  battery  for  weights 
of  stamps  and  hights  of  drop  between  the  limits  mentioned. 
This  diagram  is  based  upon  90  drops  per  minute,  and  includes 
the  friction  of  the  cam-shaft  in  the  cam-shaft  bearing,  the  friction 
of  the  cam  against  the  tappets,  the  friction  of  the  stem  against 
the  guides,  and  the  power  required  for  raising  the  stem  vertically. 
The  diagram  shows  a  line  for  each  hight  of  drop  from  4  in.  to 
10  in.  inclusive. 

To  explain  the  use  of  this  diagram,  I  give  the  following 
example:  Required  the  horse-power  to  drive  a  10-stamp  battery 
of  900-lb.  stamps,  dropping  90  drops  per  minute,  hight  of  drop 
being  7  in.  Find  the  figure  900  at  the  bottom  of  the  diagram 
under  weight  of  stamps,  follow  this  line  vertically  until  it  inter- 
sects the  7-in.  drop  line,  then  proceed  in  a  horizontal  line  to  the 
left  of  the  diagram,  where  it  will  be  found  that  the  required 
power  for  each  10-stamp  battery  is  about  17.4  horse-power. 

Another  use  of  the  diagram  is  in  finding  the  change  in  horse- 
power by  varying  the  hight  of  drop  without  changing  the  weight 
of  the  stamp.  For  example,  with  a  900-lb.  stamp,  in  changing 
the  drop  from  7  to  8  in.,  the  increase  in  power  for  each  10-stamp 
battery  is  from  17.4  to  19.4  horse-power. 

The  above  powers  are  determined  on  the  assumption  that  the 
bearings  are  properly  lubricated  and  the  stems  in  good  alinement. 

1  Abstracted  from  the  Bulletin  of  the  School  of  Mines,  Colorado;  January, 
1904. 


82 


ORE-CRUSHING  MACHINERY 


83 


10 

9 

8  •§ 

•-H 

6! 

5  £ 
4 


4 


16 


12 


500  700      800      900     1000     1100    1300 

FIG.  12. 


THE  DRY  CRUSHING  OF  ORE 

(July  5,  1902) 

The  dry  crushing  of  ore,  usually  to  a  considerable  degree  of 
fineness,  is  the  necessary  preliminary  to  a  large  number  of  metal- 
lurgical processes;  but  notwithstanding  the  antiquity  of  the  sub- 
ject and  the  extent  to  which  it  is  practised,  millions  of  tons  of 
ore  being  crushed  annually,  there  has  been  apparently  but  little 
effort  to  deduce  the  engineering  data  which  are  necessary  for 
guidance  in  the  design  and  operation  of  ore-crushing  plants, 
although  the  scientific  principles  have  been  investigated  and 
discussed  by  various  writers.  For  this  reason  the  paper  on 
"  Sampling  and  Dry  Crushing  in  Colorado/'  by  Philip  Argall, 
read  before  the  Institution  of  Mining  and  Metallurgy,  at  London, 
Feb.  20,  1902,  is  an  especially  important  contribution  to  metal- 
lurgical literature.1  Its  value  is  enhanced  by  the  facts  that  Mr. 
Argall  is  a  recognized  authority  on  this  subject  and  the  data 
now  presented  by  him  are  deduced  largely  from  his  experience 
at  the  works  of  the  Metallic  Extraction  Company  at  Cyanide, 
Colo.,  a  plant  designed  and  operated  very  successfully  for 
seven  years  by  him,  where  the  fine  crushing  of  the  hard  Cripple 
Creek  ore  was  practised  on  a  large  scale.  His  keenness  in  inves- 
tigation, clearness  of  perception  and  originality  in  overcoming 
difficulties  have  led  to  results  which  another  might  have  failed 
to  obtain.  In  presenting  the  following  abstract  of  Mr.  Argall's 
paper,  advantage  will  be  taken  of  the  opportunity  to  refer  to  an 
also  important  paper  entitled  "  Notes  on  Dry  Crushing,"  by 
N.  F.  White  (published  in  the  Transactions  of  the  Australian 
Institute  of  Mining  Engineers,  Vol.  VI,  pages  37  to  62)  wherein 
valuable  data  of  the  results  obtained  at  Mt.  Morgan,  Queensland, 
are  described.  Mr.  White's  paper,  although  much  less  compre- 
hensive and  original  than  Mr.  Argall's,  treats  of  the  subject  in 
the  same  practical  way. 

1  For  this  paper,  Mr.  Argall  was  awarded,  by  the  Institution  of  Mining 
and  Metallurgy,  the  "Consolidated  Gold  Fields  of  South  Africa,  Ltd." 
Gold  Medal  and  premium  of  forty  guineas. — EDITOR. 

84 


ORE-CRUSHING  MACHINERY  85 

Mr.  Argall  considers  that  in  crushing  material  of  which  the 
pieces  are  smaller  than  2-in.  cubes,  rolls  are  preferable  to  breakers. 
It  is  false  economy  and  bad  practice  to  attempt  a  great  reduction 
in  size  in  one  operation  or  by  means  of  one  machine.  His  own 
rule  is  never  to  exceed  the  ratio  of  4  :  1 ;  that  is,  16-in.  pieces  may 
be  broken  to  4  in.,  and  the  latter  to  1  in.  in  another  operation, 
but  he  would  preferably  provide  three  machines;  for  example, 
reducing  from  16  in.  to  5  in.  by  the  first  breaker,  from  5  in.  to 
1.5  in.  by  the  second,  and  from  1.5  in.  to  0.5  in.  by  a  set  of  rolls. 
The  capacity  of  the  various  machines  must  of  course  be  consid- 
ered, so  that  under  average  working  conditions  each  will  be  kept 
fully  supplied  with  ore.  The  coarse  breaker  may  be  followed  by 
two  fine  breakers,  and  these  by  one  or  more  roughing  rolls,  while 
in  small  plants  it  may  be  more  convenient  to  sacrifice  efficiency 
by  making  the  breaker  reduce  more  than  4  :  1,  to  avoid  the  com- 
plication of  a  second  machine  for  a  small  capacity.  Mr.  Argall 
does  not  go  into  the  details  of  coarse  crushing.  He  states,  how- 
ever, that  a  12-  by  20-in.  breaker,  reducing  to  a  maximum  size 
of  1.7  in.,  will  easily  have  a  capacity  for  25  tons  per  hour  of  ordi- 
nary quartzose  ores,  but  in  case  the  ore  is  mostly  in  large  pieces, 
say  12-in.  cubes  or  larger,  two  breakers  should  be  used  in  series 
with  a  screen  between.  Talcose  and  very  wet  ores  give  trouble; 
in  bad  cases  they  should  be  dried  before  going  to  the  breakers. 
In  referring  to  the  capacity  of  crushing  machines,  it  should  be 
remarked  how  important  a  consideration  the  specific  gravity  of 
the  ore  is.  The  Cripple  Creek  ore,  for  example,  is  andesite, 
phonolite,  and  granite,  occupying  in  lump  form  about  25  cu.  ft. 
per  ton  and  averaging  23  cu.  ft.  after  reduction  to  30-mesh 
size.  In  crushing  such  an  ore,  as  compared  with  many  sul- 
phides, the  mineral  is  not  only  harder,  but  its  volume  is  much 
greater. 

Mr.  Argall  discusses  at  considerable  length  the  methods  of 
ore  sampling,  which  are  naturally  performed  in  connection  with 
the  crushing  operation;  in  fact,  a  good  deal  of  ore  is  crushed  with 
that  object  alone  in  view.  In  this  branch  of  his  subject  we  shall 
attempt  only  to  summarize  his  conclusions.  He  condemns  unre- 
servedly the  antiquated  method  of  quartering  and  ably  points 
out  its  likelihood  of  introducing  errors.  If  the  work  must  be 
done  by  hand,  the  method  of  fractional  selection  —  that  is,  the 
reservation  of  shovelfuls  at  regular  intervals  when  the  pile  of  ore 


86  METALLURGICAL  MILL  CONSTRUCTION 

is  being  handled  for  other  purposes  —  is  not  only  more  conven- 
ient, but  also  is  far  more  accurate.  Automatic  machine  sampling 
is,  however,  superior  in  all  respects  to  hand-sampling.  This  is 
now  the  general  consensus  of  opinion.  In  sampling  ores  contain- 
ing 10  to  15  oz.  gold  per  ton,  Mr.  Argall  has  found  the  following 
ratio  between  the  average  size  of  the  ore  cubes  and  the  propor- 
tional weight  of  the  sample  to  give  accurate  results: 

Average  size,  inch 1.0000    0.2500    0.0625    0.0171 

Proportion  of  sample  % 20     1.25        0.0785    0.0050 

Pounds  from  100  tons 40,000       2500          157  10 

In  practical  work,  however,  larger  quantities  of  the  fine 
material  would  be  taken,  simply  as  an  extra  precaution.  The 
following  system  of  sampling  proved  to  be  quite  successful: 
The  ore  leaving  the  breakers  was  of  about  1  in.  average  size. 
From  100  tons  (200,000  Ib.)  40,000  Ib.  were  cut  out  as  the  first 
sample.  This  was  crushed  to  0.25  in.  size  and  4000  Ib.  was  cut 
out  by  the  second  sampler.  This  was  reduced  to  8-mesh  size 
(0.0625  in.)  and  cut  down  by  riffling  to  250  Ib.,  which  was  dried 
and  crushed  to  about  30  mesh  (0.0171  in.)  and  then  riffled  down 
to  15  Ib.  The  last  sample  was  pulverized  to  90-  or  100-mesh  and 
riffled  down  to  1  Ib.,  which  was  ground  on  the  bucking-plate  to 
pass  a  120-mesh  (0.004  in.)  sieve  and  divided  into  samples  for 
assay.  If  the  work  were  well  done  a  half  assay  ton  from  any  of 
the  120-mesh  pulps  would  check  within  0.02  oz.  (40c.)  per  ton. 
When  the  final  samples  were  passed  only  through  a  100-mesh 
sieve  there  was  often  difficulty  in  obtaining  duplicate  assays  that 
would  check.  For  cutting  out  the  large  samples  the  excellent 
apparatus  designed  by  H.  A.  Vezin,  which  is  now  in  general  use 
in  Colorado,  was  employed.  It  will  be  observed  that  the  cutting 
down  of  the  small  samples  was  done  entirely  by  riffling. 

Mr.  Argall  remarks  the  following  as  some  of  the  important 
points  to  be  remembered  in  machine  sampling: 

(1)  Take  out  a  sufficient  quantity  in  the  first  cut  to  represent 
accurately  a  thorough  sample  at  that  size. 

Where  the  ores  are  of  low  grade,  or  very  uniform  in  composi- 
tion, a  small  sample  will  suffice.  With  iron  ore,  for  example,  or 
fluxing  ores  for  blast-furnace  work,  where  it  is  important  to  keep 
them  as  coarse  as  possible,  10  per  cent,  of  ore  as  coarse  as  6. -in. 
cubes  can  be  taken  out  by  the  Vezin  sampler,  if  necessary,  and, 


ORE-CRUSHING  MACHINERY  87 

reduced  proportionally,  will  give  an  accurate  sample.  When  the 
ores  are  to  be  used  in  stamps  or  roller  mills,  and  reduced  to  an 
ultimate  state  of  fine  division,  it  is  preferable  to  reduce  them 
finer  for  the  first  cut,  and  as  a  matter  of  precaution  take  out  say 
20  per  cent,  for  the  first  sample. 

(2)  Always  crush  and  thoroughly  mix  the  ore  between  each 
cut,  unless  it  is  already  quite  fine,  and  in  this  case  the  greatest 
possible  care  must  be  exercised  in  thoroughly  mixing  before 
making  the  second  cut. 

The  very  essence  of  ore  sampling  is  never  to  cut  or  reduce 
the  ore  a  second  time  without  first  crushing  to  a  degree  of  greater 
fineness.  A  moment's  reflection  will  show  the  necessity  of  this. 
We  will  assume  a  lot  of  ore  crushed  to  cubes  of  1  in.  average 
size,  and  that  20  to  25  per  cent,  is  necessary  to  give  a  correct 
sample  at  this  size,  the  latter  (25)  per  cent,  being  of  course  taken 
as  a  matter  of  precaution.  Now  it  is  obvious  that  if  this  sample 
is  reduced  50  per  cent,  without  re-crushing,  it  simply  amounts  to 
taking  out  12J  per  cent,  in  the  first  cut,  which  with  1-in.  cubes 
we  have  found  to  be  50  per  cent,  too  small  to  give  a  correct 
sample.  It  follows,  therefore,  that  if  50,000  Ib.  are  taken  as  the 
first  cut  from  a  100-ton  lot  of  1-in.  average  cubes,  and  these  are 
then  crushed  to  J-in.  average,  3125  Ib.  will  give  as  accurate  a 
sample  at  J  in.  as  50,000  at  1  in.;  or  if  the  ore  is  all  crushed  to 
i  in.,  3125  Ib.  will  do  for  first  cut;  and  further,  that  on  a  re- 
duction to  -^Q  in.,  195  Ib.  bears  the  same  ratio  between  size  of 
cube  and  weight  of  sample  as  the  50,000  Ib.  did  to  1-in.  cubes, 
and  hence  will  give  a  correct  sample. 

Mixing  comes  next  in  importance,  more  especially  for  spotted 
ores;  for  unless  the  sample  is  well  mixed  it  will  require  a  greater 
number  of  cuts  to  give  accurate  results;  that  is,  the  speed  of  the 
cutter  must  be  greater  or  the  number  of  scoops  increased. 

When  the  sample  is  crushed  in  rolls  and  elevated  to  the 
cutter,  the  mixing  is  found  to  be  sufficient,  provided  there  is  a 
steady  feed  to  the  rolls  so  that  a  uniform  stream  passes  the  cutters 
without  intermission  or  break.  When  the  ore  is  very  fine,  two 
or  more  cuts  can  of  course  be  taken  before  crushing  finer,  but  it 
is  not  nearly  so  safe  a  method  as  that  previously  described  — 
solely  on  account  of  the  difficulty  in  retaining  a  homogeneous 
mixture,  more  particularly  when  the  ore  is  very  dry. 

(3)  Use  riffles  for  reducing  the  size  of  samples  after  leaving  j 


METALLURGICAL  MILL  CONSTRUCTION 


the  last  automatic  sampler.  Abandon  all  forms  of  "  coning  and 
quartering,"  mixing  samples  on  floors,  scraping  and  sweeping  up 
samples,  etc.,  and  thus  eliminate  these  sources  of  error  and  labor- 
wasting  devices. 

In  the  fine  crushing  of  ore  it  is  essential  to  dry  it  down  to  a 
content  of  no  more  than  1  per  cent,  water,  and  also  if  the  ore  be 
clayey  to  raise  its  temperature  to  about  250  deg.  F.  Cold  ore  of 
that  class  lies  dead  on  the  screens  and  has  a  tendency  to  choke 
them,  even  if  it  be  quite  dry;  but  when  hot  they  screen  as  well 
as  hard,  gritty  ores.  Mr.  Argall  employs  the  well-known  4-tube 
revolving  drier,  invented  by  himself.  This  drier  is  in  principle 
the  same  as  the  ordinary  cylindrical  drier,  the  products  of  com- 
bustion from  the  fireplace  at  the  discharge  end  passing  through 
the  tubes,  over  the  ore,  but  it  has  the  advantages  that  the  ore  is 
divided  into  four  thin  streams  and  the  hot  gases  are  brought 
more  closely  in  contact  with  the  ore.  The  Argall  4-tube  drier 
is  made  in  two  sizes,  No.  1  having  a  capacity  of  80  to  100  tons 
of  ore  per  day,  and  No.  2,  150  to  200  tons;  the  6-tube  driers 
have  50  per  cent,  more  capacity.  The  efficiency  of  these  driers 
is  shown  in  the  following  table: 


NAME  AND  LOCATION  OF  MILL 

NO.   OF 
DRIER 

%  WATER 

TONS   ORE 
DRIED    PER 

TONS  COAL 
USED 

REMARKS 

BEFORE 

AFTKR 

Bessie,  Telluride,  Colo.  .  .  . 

2 

8.00 

1.22 

177 

2.66 

a 

Cyanide,  Leadville,  Colo.  . 

1 

10.00 

1.00 

70 

1.00 

b 

Metallic,  Cyanide,  Colo.  .  . 

2 

4.00 

1.00 

c 

(a)  Coal,  poor  quality  of  slack,  burned  with  Jones  underfeed 
stoker;  ore  clayey. 

(b)  Coal  of  fairly  good  quality,  hand-fired;  ore  talcose  and 
clayey;  cylinders  inclined  0.75  in.  per  foot  and  driven  at  two 
revolutions  per  minute. 

(c)  Coal  good,  burned  with  American  stokers;  ore  silicious. 
The  above  data  show  an  evaporation  per  pound  of  coal  of 

4.54,  6.3  and  9  Ib.  of  water  respectively.  In  making  such  com- 
parisons, however,  it  is  necessary  to  remember  not  only  the 
difference  in  the  grades  of  the  coal,  but  also  that  clayey  ores 
require  a  higher  temperature  and  are  more  difficult  to  dry  than 
sandy  or  porous  ores. 


ORE-CRUSHING  MACHINERY  89 

The  cost  of  drying  ore  is  comparatively  little.  Assuming  an 
evaporative  effect  of  7  Ib.  water  per  pound  of  coal,  the  cost  of 
drying  100  tons  of  ore  containing  6  per  cent,  water,  leaving 
1  per  cent,  in  the  product,  is  as  follows:  1430  Ib.  coal  @  $3.00  = 
$2.14;  labor,  $2.00;  repairs  and  lubricants,  $0.43;  motive  power, 
etc.,  $0.25;  total,  $4.82,  or  approximately  5c.  per  ton. 

Mr.  Argall  calls  attention,  as  we  have  done  repeatedly,  in  this 
journal,  to  the  inaccuracy  of  specifying  the  size  of  wire  cloth  by 
the  number  of  meshes  per  linear  inch,  the  diameter  of  the  aper- 
ture, which  depends  upon  the  gage  of  the  wire  from  which  the 
cloth  is  woven,  being  the  important  thing.  Ordinarily  the 
heaviest  standard  wire  to  be  had  for  any  given  mesh  is  employed 
in  ore  milling,  but  there  are  cases  where  the  opposite  is  the  better 
practice.  As  a  general  thing  the  heavier  wire  is  the  better  for 
coarse,  gritty  ores,  but  for  soft,  clayey  ores,  likely  to  choke  up 
the  screens,  the  finer  wire  is  preferable  in  a  dry  crushing  mill. 
For  coarse  screening,  say  down  to  0.25-in.  openings,  perforated 
steel  plate  trommels  of  circular  section  give  the  best  service. 
From  0.25  to  0.10-in.,  wire  cloth  trommels,  also  of  circular  section, 
are  preferable.  For  the  finer  meshes  the  hexagonal  form  of 
screen,  of  light  construction  so  that  the  weights  or  hammers, 
when  they  fall,  will  throw  the  whole  sheet  into  vibration,  and 
thus  tend  to  keep  the  meshes  open,  are  most  advantageous. 
Heavy,  rigid  screens  are  a  mistake. 

The  proper  peripheral  speed  of  hexagonal  fine  screens  is  about 
180  ft.  per  minute.  The  angle  of  slope  should  not  exceed  10  deg. 
from  the  horizontal.  Ample  screening  capacity  should  be  pro- 
vided, making  proper  allowances  for  the  inferior  efficiency  of  dry 
sifting  screens  as  compared  with  wet  work.  In  crushing  to  30 
mesh  (0.0171  in.)  Mr.  Argall  has  found  that  in  general  work 
1  sq.  ft.  of  screen  will  deliver  about  6  cu.  ft.  of  product  per  24 
hours,  but  with  clayey  ore  the  ratio  is  likely  to  fall  to  1 :  5.  Large 
screening  surfaces  not  only  means  greater  output,  but  also  less 
repairs.  In  crushing  99,270  tons  of  ore,  the  cost  of  maintenance 
of  screens  was  2c.  per  ton.  With  respect  to  housing  the  screens 
the  following  suggestions  are  offered: 

"The  screening  process  is  usually  a  dusty  one,  in  fact  the 
most  dusty  in  the  mill.  If,  however,  the  screens  are  grouped  on 
each  floor  and  completely  housed  in,  not  in  boxes,  but  in  a  room 
large  enough  for  men  to  enter  and  walk  freely  around  the  screens, 


90  METALLURGICAL  MILL  CONSTRUCTION 

to  change  and  clean  them,  there  will  be  no  trouble  from  dust 
escaping,  particularly  if  the  room  is  connected  with  an  exhaust 
fan,  as  it  should  be.  Such  a  screen  room  would  be  closed  every- 
where air-tight,  and  have  at  most  but  two  doors,  one  on  each 
side;  it  could  be  wired  for  electric  light,  to  be  used  only  when  the 
screen  men  are  in  the  room.  The  heads  of  the  elevators  should 
be  connected  with  this  room,  or  rooms,  and  in  fact  all  points  in 
the  mill  requiring  exhaust  ventilation.  The  discharge  from  the 
exhaust  fan  should  be  conveyed  into  a  bag-house,  and  forced 
through  cotton  bags,  leaving  the  ore  particles  inside.  The  bags 
should  be  shaken  every  second  day  to  detach  the  dust,  and  thus 
prevent  the  pressure  against  which  the  fan  delivers  the  dust-laden 
air  from  increasing  above  2  ounces.  A  volume  of  20,000  cubic  feet 
of  air  per  minute  would  require  5000  square  yards  of  filtering 
fabric." 

For  the  purpose  of  fine  crushing  Mr.  Argall  is  unequivocally 
in  favor  of  rolls,  except  in  connection  with  amalgamation  pro- 
cesses, for  which  he  recommends  them  only  as  an  intermediate 
machine  between  the  breaker  and  the  stamps.  He  considers 
that  the  latter  application  would  be  advantageous,  inasmuch  as 
reducing  the  2-in.  stuff  from  a  breaker  to  0.75-in.  size  by  means 
of  rolls,  and  feeding  the  product  of  the  latter  to  the  stamps,  the 
capacity  of  the  stamps  will  be,  in  many  cases,  increased  about 
25  per  cent.,  while  the  wear  and  tear  on  them  will  be  reduced. 
In  crushing  for  the  cyanide  and  chlorination  processes,  in  which 
a  granular  product  is  desired,  stamps  would  hardly  receive  con- 
sideration at  all  in  modern  practice.  Aside  from  rolls,  about  the 
only  standard  type  of  machine  available  is  the  ball-mill,  the 
merits  of  which  Mr.  Argall  discusses  later  on.  In  ore-dressing 
works  rolls  can  be  used  in  wet  crushing  down  to  20-mesh  with 
very  good  results,  and  with  fair  results  down  to  40-mesh  if  there 
is  not  much  clayey  matter  in  the  ore.  In  considering  the  ques- 
tions pertaining  to  the  design  and  operation  of  modern  rolls,  as 
to  which  Mr.  Argall  is  a  high  authority,  it  is  best  to  use  his  own 
language : 

"  Rolls  are  usually  described  as  belted  or  geared.  Geared 
rolls  of  high  speed  are  an  abomination,  even  in  coarse  crushing. 
Belt  wheels  of  ample  size  to  transmit  the  necessary  power  should 
in  all  cases  be  used,  with  the  result  of  a  saving  in  power,  a  great 
saving  in  repairs,  better  and  more  uniform  work,  and  almost 


ORE-CRUSHING  MACHINERY  91 

entire  absence  of  the  noise  and  jar  inseparable  from  the  use  of 
geared  rolls. 

"  Rolls  as  usually  built  have  many  defects,  which  in  ordinary 
work  are  for  a  time,  while  the  machine  is  new,  passed  over;  but 
in  fine  crushing  they  immediately  give  trouble,  and  soon  become 
intolerable.  The  first  and  most  serious  of  these  defects  is  separate 
journal  boxes  for  the  sliding  roll,  each  held  in  place  with  its  own 
tension  rod  and  spring.  In  this  arrangement  it  is  impossible  to 
keep  an  even  pressure  on  the  rolls;  as,  for  example,  one  side  or 
pair  of  journals  may  be  held  up  to  the  crushing  position  with  a 
spring  pressure  of  say  30  tons,  while  the  opposite  side  may  have 
but  one-half  the  pressure,  the  result  being  unequal  opening  of 
the  roll  across  its  face,  inferior  crushing,  end  thrust  and  hot 
boxes.  Any  lack  of  parallelism  between  the  rolls  results  in  end 
thrust  and  tendency  towards  wearing  away  of  the  collars,  and 
allowing  the  rolls  to  pass  each  other,  setting  up  flanging,  and 
greatly  augmenting  end  thrust.  As  an  alleged  cure  for  this  state 
of  affairs,  we  sometimes  find  one  roll  two  or  three  inches  wider 
than  the  others,  so  that  the  narrower  one  can  wear  into  its  fellow, 
forming  a  flange  on  either  side.  This  is  a  palliative  nearly  as 
bad  as  the  disease,  and  is  in  no  sense  a  cure.  It  does,  however, 
increase  the  friction,  decrease  the  capacity  of  the  roll,  and  increase 
its  repair  bill. 

"  Rolls  should  not  only  open  parallel  across  the  face  under 
all  conditions  of  service,  but  should  also  remain  truly  level;  that 
is,  a  plane  passing  through  the  center  of  the  fixed  roll  shaft  should 
always  intersect  the  center  of  the  swinging  or  moving  roll  shaft. 
Any  departure  from  this  plane  also  tends  towards  end  thrust, 
flanging,  and  greatly  increasing  frictional  resistance  of  the  machine. 
When  the  moving  roll  is  mounted  on  any  pin- jointed  lever  ar- 
rangement, these  exact  conditions  are  not  fulfilled,  while  a  slight 
wear  of  a  pin  joint  disturbs  the  horizontality  of  the  axis  and 
increases  the  friction.  Therefore,  it  is  apparent  that  the  movable 
roll  is  best  mounted  in  a  sliding  device,  with  large  anti-friction 
surfaces.  Where  the  roll  is  mounted  on  pin-jointed  levers,  I 
consider  it  bad  practice  to  have  them  unequal  except  the  shorter 
movement  is  given  to  the  spring;  in  other  words,  the  opening  of 
the  roll  should  not  be  multiplied  on  the  spring,  but,  if  possible, 
reduced,  so  as  to  ensure  smooth  running  and  lessening  of  shock. 
All  rolls  should  have  swivel  or  ball  and  socket  journal  boxes. 


92  METALLURGICAL  MILL  CONSTRUCTION 

The  application  of  more  power  to  the  fixed  than  to  the  movable 
roll  is  not  based  on  any  good  reasoning.  Attempts  to  run  one 
roll  faster  than  the  other  are  objectionable  for  several  reasons; 
while  catalog  cuts  showing  an  8-in.  belt  on  a  3-ft.  pulley  running 
the  movable  roll  101  revolutions  per  minute,  against  the  fixed 
roll  with  a  14-in.  belt  on  a  7-ft.  pulley  at  100  revolutions,  are 
perhaps  not  more  absurd  than  some  other  attempted  roll  prac- 
tices, yet  it  has  always  struck  me  as  very  humorous. 

"There  is  a  wide  variation  in  practice  as  to  the  speed  of  rolls, 
ranging,  as  they  do,  from  the  30  or  40  ft.  per  minute  of  the  old 
Cornish  roll,  to  the  800  to  1000  feet  of  the  modern  high-speed 
rolls.  In  discussing  speed,  one  very  seldom  hears  of  graduating 
it  in  accordance  with  the  size  of  the  ore  to  be  acted  on;  yet  this  is, 
in  my  opinion,  a  fundamental  principle.  A  careful  series  of 
experiments  has  convinced  me  that  there  is  a  speed  for  each  size 
of  material  which  gives  the  maximum  capacity  with  the  minimum 
power.  These  speeds  were  correlated,  and  from  them  the  for- 
mula and  diagrams  presented  herewith  were  deduced.  I  do  not 
wish  to  be  understood  as  saying  that  these  are  the  only  correct 
speeds  at  which  rolls  should  be  operated;  but  I  do  say  they  are 
the  speeds  I  have  found  to  give  the  best  results;  that  they  are 
safe  and  reliable,  and  the  engineer  who  conforms  his  practice 
accordingly  will  not  be  disappointed. 

"In  reducing  coarse  ore  with  rolls,  I  never  exceed  a  ratio  of 
over  4:1,  crushing,  say  from  2  in.  to  J  in.,  J  in.  to  J  in.,  and  so 
on.  In  the  diagram  (Plate  13)  I  assume  a  roll  is  set  with  £-in. 
opening  between  tires,  and  crushing  from  2  in.  to  J  in.,  and  so  on 
proportionally  for  the  other  rolls.  In  each  case  the  space  between 
the  rolls  is  equal  to  the  mesh  to  which  the  roll  is  crushing.  There 
is  also,  or  rather  there  should  be,  a  relative  proportion  between 
the  diameter  of  the  rolls  and  the  size  of  the  particles  fed  to  them, 
more  particularly  in  crushing  the  larger  cubes,  as  it  is  manifest 
that  if  the  size  of  the  ore  cubes  materially  exceed  the  'angle  of 
nip,'  they  will  merely  dance  around  and  will  not  be  drawn  down 
and  crushed.  This  phenomenon  is  more  pronounced  in  the 
high-speed  rolls. 

"In  my  diagram  the  speed  curves  of  the  various  size  rolls  are 
terminated  on  the  right  by  another  curve,  which  we  may  call  the 
curve  of  nip.  Taking  the  speed  curve  for  a  42-in.  roll,  we  find  it 
terminated  by  the  curve  of  nip  on  the  2-in.  cube  line  at  the 


ORE-CRUSHING  MACHINERY 


93 


twenty-eighth  ordinate,  showing  that  to  crush  2-in.  cubes  we 
require  a  42-in.  roll,  and  that  its  proper  speed  is  28  revolutions 
per  minute.  Taking  a  26-in.  roll,  we  find  the  maximum  sized 
feed  1.25  in.,  the  speed  for  these  cubes  55  revolutions  per  minute, 
while  for  J-in.  cubes  the  speed  is  73  revolutions,  for  0.25-in. 
cubes,  88,  and  for  0.05  in.,  108  revolutions  per  minute. 

"The  theoretical  capacity  of  rolls  might  be  described  as  the 
number  of  cubic  feet  per  hour  that  would  be  rolled  out  in  a  ribbon, 
the  length  being  the  peripheral  travel  of  the  roll  in  one  hour, 
the  width  that  of  the  roller  faces,  the  thickness  being  the  distance 


Diagram 

Showing  proper  Speed  of  Rolls 
and  Maximum  Size  of  Feed 


D  _  DUm.of  Roll*  In  Inches  N  „  No.R.P.11. 

P  _  Peripheral  Speed  in  Feat  per  Minute 
8  _  She  in  Inches  Huimun  O'e  Cub. 
.  SIM  in  Inches  Maxim un  Cub*  for 
given  Diameter  of  Roll 


0.1    0.2    0.8   0.4     0.6    0.6    0.7     0.8    0.9    1.0     U    L«     1.8     U 
Size  of  Cube  in  Inches 

FIG.  13. 


U     L<    1.7     1.8 


between  the  rolls;  this  we  may  express  mathematically  as 
[PXWXSX  60]  -v-1728  =  C,  wherein  P  represents  the  peripheral 
speed  in  inches  per  minute,  W  width  of  the  roll  face  in  inches, 
S  space  between  rolls  in  inches,  C  capacity  in  cubic  feet  per  hour. 
Such  a  ribbon  could  not  of  course  be  homogeneous;  it  would  have 
spaces  and  cavities  unfilled,  and  would  consist  of  particles  of 
every  size  from  the  largest  that  could  pass  through  the  space 
between  the  rolls  down  to  the  finest  dust. 

"Let  us  take  the  case  of  a  26-  by  15-in.  roll,  60  revolutions 
per  minute,  crushing  from  1  in.  to  J  in.     The  theoretical  capacity 


94  METALLURGICAL  MILL  CONSTRUCTION 

is  by  the  formula  at  once  found  to  be  589  cu.  ft.  per  hour,  taking 
the  mean  diameter  of  the  roll  at  24  in.  But  how  shall  we  find 
the  actual  capacity  of  these  rolls  in  cubic  feet  per  hour  of  finished 
product?  It  is  perhaps  best  to  be  frank  and  state  that  we  cannot, 
as  there  are  too  many  variables  to  be  taken  into  consideration; 
but  we  can  closely  approximate  it. 

"Following  up  the  case  I  have  taken,  the  maximum  size 
cubes  are  1  in.,  th~  minimum  just  a  little  coarser  than  £-in.  as 
fed  to  the  roll.  Now,  as  different  varieties  of  ores  do  not  break 
alike,  one  sort  may  have  as  much  as  15  per  cent,  more  of  say 
j-in.  cubes  in  the  feed  than  another,  and  would  consequently 
give  a  larger  percentage  of  finished  product  after  passing  through 
the  rolls,  and  so  on.  My  experiments  have,  however,  shown  that 
there  is  a  very  close  relation  between  the  percentage  of  reduction 
and  the  amount  of  finished  product  for  any  given  ore.  Ity 
percentage  of  reduction  I  mean  an  inch  cube  reduced  to  f  in.  is 
25  per  cent,  reduction;  to  J  in.,  50  per  cent,  and  to  J  in.,  75  per 
cent. 

"  Referring  to  diagram,  Plate  14,  on  the  left,  an  inch  is  divided 
by  horizontal  lines  into  100  parts,  the  scale  extending  two  inches 
in  hight;  next  there  is  a  series  of  diagonal  lines  to  give  the  per- 
centage of  reduction  at  the  given  sizes ;  and  lastly  a  heavy  diagonal 
line  marked  '  Percentage  of  finished  product  for  given  percentage 
of  reduction.'  This  curve  of  finished  product  I  have  fixed  from 
actual  experiments  with  quartzose  ores  of  medium  crushing 
qualities.  I  consider  it,  therefore,  correct  for  average  conditions 
with  first-class  rolls.  A  few  experiments,  however  (say  three), 
will  enable  the  engineer  to  plot  this  curve  for  any  particular  ore, 
and  thereafter  he  can  quite  closely  determine  the  actual  capacity 
of  any  given  roll  on  that  particular  ore. 

"Applying  this  diagram  to  our  specific  case,  1  in.  to  \  in. 
Following  the  diagonal  line  from  1  in.  on  the  left,  we  find  it 
intersects  the  J-in.  horizontal  line  at  the  ordinate  marked  75  per 
cent,  reduction,  showing  that  the  maximum  reduction  in  the 
crushing  process  has  been  75  per  cent.  Taking  75  per  cent- 
reduction  on  the  right  hand  of  the  diagram,  and  following  the 
horizontal  line,  we  find  it  intersects  the  curve  of  finished  product 
at  the  30  per  cent,  ordinate,  showing  that  for  75  per  cent,  reduc- 
tion the  finished  product  per  hour  is  30  per  cent,  of  the  theoretical. 
The  latter  we  have  previously  seen  is  589  cu.  ft.  per  hour,  30  per 


ORB-CRUSHING  MACHINERY 


95 


cent,  of  which  gives  the  cubic  feet  per  hour  of  finished  product 
as  176  cu.  ft.,  and  so  on  for  any  ratio  of  reduction  shown  of  the 
diagram. 

"  Diagram  Plate  15  shows  the  capacity  in  cubic  feet  per  hour 
of  various  size  rolls,  running  at  the  speeds  most  suitable  for  the 
size  of  the  feed  they  are  assumed  to  receive,  compiled  from 
Diagrams  13  and  14. 


5S*  CO*  65*70*  75%    80*  853  80*95#100* 


Roll  Diagram 

Showing 

Percentage  of  Reduction 


Corresponding  Percentage 
of  Finished  Production 

October  1901         **"«>  ArgM, 


6*    10}}   16*  20*  25*  30  *35*  40  *  45  #60  #66  #60*  65*  70  }f  75*80*85*90*06*100* 
Percentage  of  Reduction 

FIG.  14. 

"These  diagrams  are  figured  in  cubic  feet  per  hour,  which,  in 
my  opinion,  is  the  only  correct  basis  of  comparison  between  ores. 
It  is  obvious  that  a  roll  crushing  5  tons  of  ore  per  hour,  weighing 
85  Ib.  per  cubic  feet  in  the  crushed  or  finished  state,  would  mani- 
festly crush  10  tons  per  hour  of  material  weighing  170  Ib.  per 
cubic  feet,  assuming  the  crushing  condition  of  both  ores  is  the 
same." 


96 


METALLURGICAL  MILL  CONSTRUCTION 


Mr.  Argall  gives  some  interesting  data  as  to  the  excellent  rolls 
designed  by  himself.  He  states  that  one  set  of  these,  which  has 
been  in  hard  service  for  nearly  two  years,  day  and  night,  has 
neither  developed  defects  nor  suggested  improvements.  For  six 
months  it  was  operated  at  a  speed  of  900  ft.  per  minute,  crushing 
from  0.1  to  0.02  in.,  but  was  afterward  reduced  to  a  speed  of 
750  ft.  to  conform  to  the  practice  of  that  particular  mill.  All 
rolls,  except  coarse  or  roughing  rolls,  taking  the  ore  from  the 
breakers,  should  be  provided  with  mechanical  feeders.  From 
0.25  in.  upwards,  the  stream  should  not  exceed  in  thickness  the 


1900  1800  1700  1600  1500  1400  1300  1200  1100  1000  900 


700  «00  600  400  300  200  100 


2000  1900  1800  1700  1600  1600  1400  1300  1200  1100  1000  900  800  70*  600  600  4«0  300  200  100 
Roll  Capacity  in  Cubic  Feet  per  Hour 

FIG.  15. 

maximum  faces  of  the  cubes;  below  this  size,  however,  thicker 
streams  can  be  used,  on  the  principle  that  Mr.  Argall  calls  "  choke 
feed/'  so  that  the  ore  particles  are  crushed  upon  each  other  in 
passing  the  point  of  contact,  and  the  capacity  of  the  rolls  is  very 
much  increased.  A  26-  by  15-in.  roll  at  110  revolutions,  crushing 
from  0.1  to  0.02  in.,  has  a  theoretical  capacity  of  only  86  cu.  ft. 
per  hour,  about  30  cu.  ft.  of  finished  product,  whereas  if  run 
with  choke  feed  0.25  in.  thick,  its  capacity  will  be  75  cu.  ft,  per 
hour  to  0.02  in.,  using  in  each  case  first-class  rolls.  The  space 


ORE-CRUSHING  MACHINERY  97 

between  the  boxes  of  the  movable  and  fixed  rolls  on  either  side 
should  be  filled  up  solid  with  chuck  plates  of  different  thickness, 
and  one  wedge  plate  to  give  the  fine  adjustment.  The  rolls  are 
next  spaced  to  about  the  size  of  the  finished  cubes,  say  0.02  in.; 
the  tension  rods  are  then  screwed  up  to  the  crushing  pressure 
desired.  This  pressure  does  not  come  on  the  journals,  but  on 
the  chuck  plates;  the  rolls  can  then  be  revolved  without  touching 
each  other,  but,  immediately  the  0.25  in.  " choke  feed"  is  turned 
on,  they  are  forced  apart  against  the  accumulating  spring  pressure, 
and  the  ore  is  crushed  upon  itself,  and  also  against  the  faces  of 
the  rolls.  Mr.  Argall  used  rolled  steel  tires  2£  in.  thick,  giving 
2  in.  of  wear.  They  cost  8c.  per  pound,  or  rather  averaged  8c. 
per  pound  during  a  period  when  40,000  tons  were  crushed,  the 
cost  per  ton  for  tires  being  $0.0107  =  2.14  oz.  per  ton  crushed; 
during  the  preceding  half  year  46,000  tons  were  crushed  for  a 
tire  cost  of  $0.0256  per  ton;  the  average  was  therefore  $0.0181 
per  ton  crushed,  or  3.62  ounces. 

Babbitt  is  better  for  roll  bearings  than  bronze;  it  is  also  much 
cheaper.  Where  ball  and  socket,  or  swivel  boxes  are  used,  as 
they  should  be  on  all  rolls,  the  boxes  are  preferably  re-babbitted 
each  time  the  tires  are  changed.  It  is  important  to  have  but  one 
size  of  rolls,  so  that  fewer  stores  are  required,  and  one  extra  set 
of  shafts  and  shells  with  swivel  boxes  can  be  used  in  any  of  the 
rolls.  In  this  way  shells  can  be  changed,  turned  up,  and  boxes 
babbitted  at  leisure;  and  every  time  a  change  is  made  in  the  mill, 
the  shafts  have  new  babbitt  bearings  to  run  in.  The  adoption  of 
this  method  obviates  all  trouble  from  hot  boxes. 

Mr.  Argall  emphasizes  the  importance  of  gradual  comminution 
by  means  of  a  series  of  rolls,  with  screens  interposed  between 
each  set,  as  a  fundamental  principle  in  the  fine  crushing  ore,  and 
criticises  the  so-called  unit  system  described  by  John  E.  Rothwell 
in  "The  Mineral  Industry,"  Volume  IX,  page  360,  pointing  out 
that  it  is  more  expensive  in  first  cost,  operation,  and  maintenance 
than  a  system  designed  for  gradual  comminution,  and  is  not  after 
all  a  complete  unit,  it  being  admitted  of  course  that  the  unit 
system  is  a  good  thing  if  carried  out  in  its  entirety.  However, 
the  mill  designed  for  gradual  comminution  is  capable  of  such  & 
development,  and  in  fact  in  large  installations  is  commonly  so 
arranged. 

One  of  the  most  interesting  parts  of  Mr.  ArgalPs  paper  is  that 


98  METALLURGICAL  MILL  CONSTRUCTION 

in  which  he  outlines  the  design  of  a  plant  capable  of  crushing 
400  tons  per  24  hours  of  ordinary  quart zose  ore  to  pass  a  26- 
mesh  screen  (No.  26  wire)  and  estimates  the  cost  of  its  operation. 
Such  a  plant  is  best  arranged  in  duplicate,  200  tons  per  day 
making  a  convenient  unit,  which  will  be  capable  of  independent 
operation.  For  coarse  crushing  and  sampling,  a  12-  by  20-in. 
breaker,  reducing  to  1.7-in.  size,  is  provided,  giving  an  easy 
capacity  of  25  tons  per  hour  with  ordinary  ore;  in  case  the  ore 
comes  mostly  in  lumps  of  12-in.  or  more,  however,  two  breakers 
should  be  used  in  series  with  a  screen  between  them.  Where 
talcose  and  very  wet  ores  are  to  be  sampled  in  quantity,  a  drier 
should  be  provided,  as  it  is  often  impossible  to  crush  and  sample 
such  ores  in  their  wet  state,  and  in  bad  cases  they  should  be  dried 
before  going  to  the  breakers. 

Following  the  breaker  or  breakers,  a  36-in.  by  16-in.  roll,  at 
35  revolutions  per  minute,  will  give  about  600  cu.  ft.  per  hour 
through  a  0.75-in.  screen.  For  sampling  purposes,  the  product 
of  the  36-in.  roll  is  passed  over  a  Vezin  sampler,  and  25  per  cent, 
taken  out  for  the  sample,  say  120  cu.  ft.  per  hour,  which  should 
be  deflected  to  a  26-  by  15-in.  roll  to  be  crushed  to  3-mesh  10  wire, 
0.1983  in.,  or,  in  round  numbers,  0.20  in.  At  this  size  about  6 
per  cent,  is  ample  for  a  correct  sample,  but,  to  be  quite  safe,  one- 
tenth  or  12  cu.  ft.  per  hour  may  be  cut  out;  if  the  ore  does  not 
contain  over  5  per  cent,  moisture,  the  sample,  2J  per  cent,  of  the 
original,  can  be  passed  directly  to  a  fine  grinder,  reducing  it  to 
10-mesh  18  wire,  0.0525  in.,  and  again  cut  to  one-tenth  =  1.2 
cu.  ft.  per  hour,  or  0.2  per  cent,  of  the  original  volume;  if  damp, 
the  sample  is  then  dried  and  ground,  then  passed  over  a  small 
Vezin  sampler,  or  riffled,  as  found  most  desirable,  being  finally 
finished  in  the  manner  previously  described. 

The  Vezin  sampler  with  the  necessary  operating  gear  costs 
about  $100.  It  requires  a  fall  of  about  6  ft.  It  can  be  installed, 
together  with  one  set  of  rolls,  a  sample  grinder,  and  a  riffle  sampler 
for  $500  to  $750. 

Such  a  sampling  works  should  easily  handle  200  tons  in  10 
hours,  provided  the  lots  are  of  50  to  100  tons  each.  Time  is 
always  lost  in  cleaning  up  between  two  separate  lots  of  ore,  and 
must  be  allowed  for.  Two  such  units  will  take  care  of  the  sam- 
pling of  400  tons  per  day  of  10  hours  with  comparative  ease.  It 
is  best  to  do  all  the  sampling  in  the  daytime.  The  methods  of 


ORE-CRUSHING  MACHINERY  99 

\veighing  the  ore  and  determining  its  moisture  contents  at  the 
works  of  the  Metallic  Extraction  Company  were  as  follows:  The 
ore  was  usually  weighed  on  railroad  track  scales  with  self-regis- 
tering beams;  when  the  beam  is  balanced,  a  soft  paper  card  is 
slipped  into  a  slot  and  the  lever  pulled  down,  stamping  the  gross 
weight  on  the  card.  The  car  number,  lot  number,  and  date  are 
then  written  on  the  card,  which  is  filed  away  until  the  car  returns 
unloaded,  when  the  same  operation  is  repeated  for  the  tare.  The 
weighmaster  enters  the  weights  in  his  book  and  sends  the  card 
to  the  settlement  clerk,  who  keeps  it  until  the  lot  is  settled  for. 
The  card  helps  to  settle  many  disputes  as  well  as  prevent  errors 
in  reading  the  beam.  The  moisture  sample  is  taken  from  the 
rejected  portion  of  the  ore  passing  the  cutters,  say  three  times 
for  each  car,  taking  equal  quantities  and  placing  them  in  a  can. 
When  the  last  is  taken,  the  can  is  shaken  to  mix  the  ore  and  1 
Ib.  is  then  weighed  up  in  the  presence  of  the  seller,  packed  in  a 
tray  and  put  in  a  steam-heated  drying  closet  and  kept  there, 
locked  up,  usually  for  24  hours,  when  it  is  weighed  again  in  the 
presence  of  the  seller.  In  the  case  of  talcose  ores,  which  are 
difficult  to  put  through  the  crushers  without  a  preliminary  drying, 
the  moisture  sample  is  best  taken  from  the  car  immediately  after- 
weighing. 

Each  unit  of  the  fine  crushing  plant  will  comprise  one  drier, 
three  elevators,  and  four  sets  of  26-  by  15-in.  rolls,  with  the  neces- 
sary screens,  etc.  The  rolls  are  arranged  in  series,  a  reducing 
from  0.75  to  0.25  in.,  b  from  0.25  to  0.1085  in.,  c  and  d  from 
0.0185  to  0.02  in.  Roll  a,  at  65  r.  p.  m.,  will  give  a  finished  product 
of  222  cu.  ft.  per  hour,  of  which  60  cu.  ft.  should  pass  a  0.1085-in. 
hole  (5-mesh  screen)  and  wrill,  therefore,  go  directly  to  rolls  c  and 
d,  leaving  162  cu.  ft.  per  hour  for  roll  6.  Roll  b,  at  90  r.  p.  m., 
will  give  160  cu.  ft.  per  hour  through  a  5-mesh  screen.  Of  the 
material  reduced  to  5-mesh  size,  60  +  160  =  220  cu.  ft.  per  hour, 
75  cu.  ft.  will  already  be  pulverized  to  0.02-in.  size,  so  that  rolls 
c  and  d  will  have  to  take  care  of  220  —  75  =  145  cu.  ft.  per  hour. 
These  rolls  at  110  r.  p.  m.,  with  0.25-in.  choke  feed,  will  each 
finish  75  cu.  ft.  per  hour  under  ordinary  working  conditions. 
The  capacity  of  the  four  sets  of  rolls,  reducing  from  0.75  to  0.02 
in.,  will  be,  therefore,  220  cu.  ft.  per  hour  =  9.5  tons  (reckoning; 
87  Ib.  per  cu.  ft.),  which  will  correspond  to  200  tons  in  about  21 
hours,  or  at  any  rate  easily  in  22  hours.  The  power  required 


100  METALLURGICAL  MILL  CONSTRUCTION 

Will  be  as  follows:  Coarse  crushing  and  sampling,  35  indicated 
horse-power;  fine  crushing,  50;  friction  of  engine  and  shafting, 
20;  total,  105  indicated  horse-power.  The  coarse  crushing  and 
sampling  mill  require  70  indicated  horse-power  while  running, 
and  a  power  plant  large  enough  to  allow  for  that  must  be  pro- 
vided for  each  unit ;  this  part  of  the  plant  will  run  only  half  time, 
however,  which  gives  an  average  of  35  indicated  horse-power 
per  24  hours.  In  crushing  200  tons  of  ore  to  0.02-in.  size  in  24 
hours,  the  work  of  1  indicated  horse-power  is  400,000  -5-  (24  X 
105)  =  158.73  Ib.  per  hour.  In  the  fine  crushing  alone  it  is  400,- 
000  H-  (24  X  50)  =  333  Ib.  per  hour.  These  data  are  from 
actual  results  in  practice.  In  comparing  the  efficiency  of  crush- 
ing plants,  it  is  obviously  necessary  to  reckon  all  the  power  re- 
quired; not  merely  that  for  the  crushing  machines  themselves,  but 
also  for  their  accessories,  such  as  screens,  elevators,  etc.  It  will 
be  observed  that  Mr.  ArgalPs  figures  are  based  on  the  total  power 
requirement.  Mr.  Argall  is  also  precise  in  reducing  his  results 
to  pounds  per  hour,  which  is  a  definite  statement,  whereas  the 
expression  of  tons  per  day  is  not.  In  the  latter  case  the  reader 
is  left  in  doubt  as  to  whether  the  ton  is  of  2000,  2204.6  or  2240  Ib., 
while  the  day  may  be  anything  —  8,  10,  12,  20,  or  24  hours. 

The  cost  of  crushing  400  tons  of  ore  per  day  to  0.02-in.  size 
in  such  a  two-unit  plant  will  be  as  follows:  Coarse  crushing  and 
sampling  —  labor,  $0.04325;  waste  and  lubricants,  $0.00620; 
brooms  and  brushes,  $0.00060;  tools,  $0.00210;  sundries,  $0.00060; 
total  operating  expense,  $0.05275  per  ton.  The  maintenance 
will  come  to  $0.05420,  divided  as  follows:  Labor,  $0.0232;  fittings, 
$0.0006;  nails,  bolts,  and  screws,  $0.0010;  timber,  $0.0015;  iron 
arid  steel,  $0.0017;  belts  and  lacing,  $0.0041;  castings  (pulleys, 
gear,  etc.),  $0.0002;  brass  and  babbitt,  $0.0003;  elevator  buckets 
and  bolts,  $0.0018;  chain  and  sprockets,  $0.0014;  conveyors, 
$0.0022;  roll  shells,  $0.0020;  crusher  repairs,  $0.0114;  clutches, 
$0.0008;  sundry  items,  $0.002.  The  total  cost  of  maintenance 
and  operation,  not  including  power  and  general  expense,  is, 
therefore,  10.695c.  per  ton.  The  labor  in  operation  per  shift  of 
10  hours  is  as  follows:  One-half  time  of  foreman,  $2.50;  2  men  at 
breakers,  $4;  2  men  at  samplers  and  conveyors,  $4;  head  sampler, 
'$3;  assistant  sampler,  $2;  roustabout,  $1.80;  total,  $17.30;  $17.30 
-f-  400  =  $0.04325.  It  is  assumed  that  the  ore  is  delivered  to 
the  breakers. 


ORE-CRUSHING  MACHINERY  101 

Fine  Crushing.  —  The  operating  expense  per  ton  of  ore  is  as 
follows:  Labor,  $0.07625;  lubricants  and  waste,  $0.01510;  tools, 
brushes,  and  brooms,  $0.01300;  coal  for  drying,  $0.02140;  total, 
$0.12575.  The  cost  of  maintenance  is  as  follows;  Labor,  $0.0446; 
nails  and  screws,  $0.0005;  lumber,  $0.0004;  brick  and  fire-clay, 
$0.0015;  iron  and  steel,  $0.0118;  belts  and  lacing,  $0.0243;  pul- 
leys and  gears  (castings),  $0.0102;  babbitt  and  brasses,  $0.0623; 
screen  cloth  and  perforated  sheets,  $0.0206;  elevator  buckets 
and  bolts,  $0.0088;  chains  and  sprockets,  $0.0021;  conveyors, 
$0.0017;  roll  shells,  $0.0181;  clutches  and  couplings,  $0.0006; 
sundry  fittings,  $0.0025;  total,  $0.15000.  The  grand  total  is 
therefore  $0.12575  for  operation  plus  $0.15000  for  maintenance, 
or  $0.27575.  The  crew  of  the  fine  crushing  department  per  shift 
of  8  hours  is  one  man  at  the  feeders  and  driers,  $2;  one  man  at 
the  8  sets  of  rolls,  $2.50;  one  man  oiling  and  sweeping,  $2;  one 
man  attending  to  screens,  $2;  total  per  shift,  $8.50.  Three  shifts, 
at  $8.50,  together  with  the  wages  of  foreman  at  $5,  come  to 
$30.50,  and  $30.50  ^  400  =  7.625c.  per  ton. 

The  total  cost  is,  therefore,  summarized  as  follows:  Coarse 
crushing  and  sampling,  10.695c.  per  ton;  fine  crushing,  27.575c; 
power  (estimating  $72  per  indicated  horse-power  per  annum, 
the  engine  being  non-condensing),  10.500c.;  total,  48.77c.,  or, 
say  50c.  in  round  numbers.  This  does  not  include  general  ex- 
pense (administration,  insurance,  taxes,  etc.),  or  any  deduction 
for  amortization. 

It  is  interesting  to  compare  the  above  figures  with  the  data 
communicated  by  N.  F.  White  as  to  the  results  at  Mount  Morgan, 
where  fine  crushing  is  done  both  by  means  of  rolls  and  by  ball- 
mills,  the  installation  of  the  latter  for  this  purpose  being  perhaps, 
the  most  complete  and  extensive  that  has  yet  been  made.  The. 
Mount  Morgan  ore,  which  is  soft  and  friable,  containing  about. 
10  per  cent,  of  hard  quartz,  is  treated  by  the  chlorination  process.. 
The  first  plant  installed  comprised  a  Blake  breaker,  a  drier,  and 
four  sets  of  Krom  rolls,  together  with  the  necessary  screens, 
elevators,  etc.  The  success  of  this  plant  led  to  the  installation 
of  another  one,  consisting  of  two  units,  each  equipped  with  a 
Krom  breaker  and  four  sets  of  Krom  rolls,  arranged  in  series. 
The  dimensions  of  the  rolls  and  the  distance  of  their  faces  apart 
were  as  follows:  No.  1,  26  by  15  in.,  f  in.;  No.  2,  26  by  15  in., 
3-16  in.;  No.  3,  30  by  16  in.,  1-16  in.;  No.  4,  30  by  16  in.,  close 


102 


METALLURGICAL  MILL  CONSTRUCTION 


together.  The  ore  was  crushed  to  pass  a  20-mesh  brass  wire 
.screen,  data  not  given,  but  with  apertures  probably  of  about 
0.025  in.  The  cost  of  crushing  per  ton  of  ore  was  as  follows: 


OPERATION 

MILL  NO.  I 

MILL  NO.  2 

Wages  

S.              D. 

2       6.40 

S.             D. 

2      6.20 

Stores  

2.80 

3.90 

Firewood 

1      2.50 

2      0  50 

'Cartage           .                    ...                    

2.30 

Water        

0.57 

0.52 

Electric  light  

1.43 

0.59 

•General  expense 

1.18 

0  57 

Total         .... 

4      5.18 

5      0.28 

MAINTENANCE 

Waees 

352 

520 

Stores 

1067 

10  80 

Timber                   .           

0.22 

0  18 

Mechanics'  work  

6.28 

5.21 

Total  .                    . 

1      869 

1      9  39 

Orand  total..         

6      1  87 

6      967 

In  the  new  mill  the  rolls  were  driven  at  112  r.  p.  m.  The 
"wear  of  the  tire  steel  was  0.108  Ib.  per  ton  of  ore  crushed.  The 
capacity  was  125  tons  per  day,  and  100  indicated  horse-power 
was  required.  (It  is  not  stated  in  this  paper  whether  the  tons 
meant  are  of  2240  or  2000  Ib.,  but  presumably  they  are  the 
iformer.)  Mr.  Argall  computes  that  the  work  done  at  Mount 
Morgan,  in  crushing  to  0.025-in.  size,  is  116.66  Ib.  per  indicated 
tiorse-power  hour,  as  compared  with  243.6  Ib.  per  indicated  horse- 
power hour  in  the  plant  (of  practically  the  same  equipment  as 
to  number  of  machines),  which  he  has  outlined,  crushing  to 
O.025  in.,  and  presents  these  figures  as  a  comparison  between  the 
latest  Colorado  practice  with  modern  rolls  and  the  Mount  Morgan 
•experience  with  less  efficient  machines.  This  assumes,  of  course, 
that  the  Mount  Morgan  ore  is  of  about  the  same  weight  per  cubic 
foot  of  finished  product  and  of  about  the  same  crushing  quality 
as  the  Colorado  (Cripple  Creek)  ore.  We  think,  however,  that 
the  data  are  lacking,  not  merely  as  to  the  character  of  the  ore, 
but  also  as  to  the  details  of  the  Mount  Morgan  practice,  to  justify 
this  deduction  of  more  than  double  duty  per  indicated  horse- 
,  inasmuch  as  the  Krom  rolls,  although  now  greatly  im- 


ORE-CRUSHING  MACHINERY  103 

proved  upon  by  others,  are,  nevertheless,  a  high  class  of  machine. 
It  is  obvious  that  Mr.  Argall  recognizes  the  deficiency  in  data  as 
to  the  Mount  Morgan  practice  and  makes  his  computations  rather 
for  the  purpose  of  illustrating  the  high  efficiency  of  modern 
American  roll-crushing  than  as  an  absolute  comparison  of  types 
of  rolls. 

In  a  year's  run  with  the  8-roll  mill  at  Mount  Morgan,  during 
which  45,844  tons  of  ore  were  crushed,  the  average  cost  of  opera- 
tion and  maintenance,  not  including  electric  light,  water  supply, 
breaking  and  drying,  and  presumably  no  general  expense,  was 
as  follows:  Screens  —  steel  and  brass  wire-cloth,  2.62d.;  flannel 
and  calico,  0.02d.;  belting  and  sundries,  0.86d.;  total,  3.50d.;  rolls  — 
new  tires,  2.01d.;  repairs,  1.21d.;  belting  and  sundries,  0.87d.; 
waste,  0.17d.;  oil  and  kerosene,  0.46d.;  tallow,  0.75d.;  total, 
5.47d.;  elevators  —  buckets,  belting,  etc.,  1.87d.;  sundries,  0.27d.; 
total,  2.14d.;  wages,  2s.  11.25d.;  grand  total,  3s.  10.36d.  The 
labor  per  shift  of  8  hours  was  as  follows:  Two  men  at  breakers, 
1  man  at  the  two  driers,  2  men  at  the  8  rolls,  1  man  at  screens, 
elevators,  etc. ;  1  overseer,  1  spare  man,  and  one-third  of  the  super- 
intendent's time. 

When  the  sulphide  ore  was  opened  at  Mount  Morgan,  it  was 
found  that  the  wear  and  tear  on  the  rolls  increased  excessively  in 
crushing  the  much  harder  ore,  while  the  output  of  the  plant  was 
reduced.  This  led  to  the  installation  of  a  plant  of  Krupp  ball- 
mills,  at  first  experimentally  with  four  No.  4  machines.  Although 
the  ore  was  crushed  in  these  to  pass  a  35-mesh  screen,  the  cost 
per  ton  was  very  much  less  than  in  the  roll  plant.  In  a  year's 
run  the  four  mills  put  through  23,788  tons  of  ore,  and  the  working 
time  having  been  313  days,  the  average  per  mill,  per  day,  was 
19  tons.  Each  mill  required  about  10  indicated  horse-power. 
The  success  of  this  plant  led  to  the  installation  of  another  and 
larger  one,  comprising  16  No.  5  mills,  arranged  in  groups  of  four, 
each  group  having  its  own  breaker,  revolving  drier,  and  the  neces- 
sary elevators,  etc.  This  plant  is  used  for  the  treatment  of  the 
low-grade  oxidized  ore  of  the  mine,  the  same  which  had  previously 
been  crushed  in  the  roll  plant. 

The  comparative  cost  of  crushing  oxidized  ore  at  Mount 
Morgan  with  rolls  and  ball-mills,  reducing  the  ore  in  each  case  to 
0.025  in.,  based  on  one  year's  work,  amounting  to  45,844  tons  for 
the  rolls  and  130,776  tons  for  the  Krupp  ball -mills,  was  as  follows: 


104 


METALLURGICAL  MILL  CONSTRUCTION 


RUNNING   EXPENSES 

8   KROM   ROLLS 

l6   BALL-MILLS 
NO.  5 

Wages  

S. 

2 
0 
2 

D. 

6.20 
3.90 
0.50 

S. 
1 

0 
0 
0 
0 
0 
0 
0 
0 

0.034 
2.766 
ft.  538 
3.817 
0.223 
0.332 
0.068 
0.235 
1.317 

Stores 

Firewood 

Coal 

General  expenses  

0 
0 
0 

0.57 
0.59 
0.52 

Electric  light  

Water  supply 

Cartage 

Inclined  tram  

Total  running  expense  

5 

0 
0 

0.28 

5.20 
10.800 

2 

0 
0 
0 
0 
0 

6.330 

3.325 
10.493 
0.038 
2.906 
0.015 

MAINTENANCE  (REPAIRS) 

Wages. 

Stores            .       .    . 

Cartage  

Mechanics'  work  

0 
0 

5.210 
0.180 

Timber  

Total  expense  of  maintenance.. 

1 

9.39 

1 

4.777 

Grand  totals  

6 

9.67 

3 

11.107 

The  crew  of  the  roll  plant  comprised  8J  men  per  shift,  as  pre- 
viously stated.  That  of  the  ball-mill  plant  consisted  of  4  men  at 
the  breakers,  2  men  at  the  driers,  3  men  at  the  mills,  1  man  and 
1  boy  in  the  engine-room,  and  two  men  in  the  boiler-room,  besides 
1  man  and  a  boy  for  general  work,  a  total  of  15  men  per  shift;  but 
it  will  be  observed  that  this  includes  the  labor  in  the  steam  and 
power  plant,  which  is  not  included  in  the  statement  as  to  the  roll 
plant,  though  the  cost  of  power  is  evidently  included  in  the  total 
of  6s.  9.67d.  per  ton.  The  No.  5  ball-mills  in  this  plant  crush  an 
average  of  about  24  tons  per  24  hours  to  pass  a  20-mesh  screen. 

Previously  in  his  paper,  Mr.  White  stated  that  the  plant  of  four 
No.  4  mills  crushed  19  tons  of  sulphide  ore  per  24  hours  to  pass  a 
35-mesh  screen.  This  relatively  high  performance  is  probably  ac- 
countable to  the  greater  specific  gravity  of  the  ore.  The  method  of 
reckoning  the  product  of  crushing  machines  by  the  cubic  feet, 
which  is  adopted  by  Mr.  Argall,  gives  more  accurate  data  and  is 
never  misleading.  The  character  of  the  ore,  of  course,  makes  con- 
siderable difference  in  the  duty  of  crushing  machines.  In  crushing 
with  rolls  at  Cyanide,  Colo.,  the  ores  varied  from  hard  jasper  and 
chalcedony  to  soft  andesites  and  porphyries,  and  included  granite, 
phonolite,  and  quartz  rock.  Granite  proved  to  be  the  most  easily 
crushed,  quartz  next;  the  softer  ores  were  less  satisfactory.  Rolls 


ORE-CRUSHING  MACHINERY 


105 


crush  exactly  on  the  same  principle  as  rock  breakers,  in  which  soft 
and  tough  ores  give  low  capacity,  while  hard,  brittle  ores,  that  break 
with  a  snap,  seldom  give  low  capacity. 

The  power  required  by  the  plant  of  16  mills  was  as  follows: 
Sixteen  ball-mills  at  13  indicated  horse-power,  208;  4  breakers 
26;  4  driers  and  elevators  at  6  indicated  horse-power,  24;  line 
shaft,  countershaft,  etc.,  14;  friction  of  engine  at  18  per  cent,  of 
total  of  previous  items,  49;  total,  321.  The  capacity  of  the  mill 
is  400  tons  per  24  hours,  and  the  work  of  1  indicated  horse-power 
is  116.29  Ib.  per  hour  as  the  maximum,  but  the  average  is  368 
tons  and  the  work  of  1  indicated  horse-power  per  hour  107.33  Ib. 
The  power  is  developed  by  means  of  a  triple-expansion  horizontal 
engine  of  24-in.  stroke  and  cylinders  of  15,  24,  and  39  in.  diameter. 
This  engine  is  directly  connected  with  the  line  shaft.  The  steam 
is  supplied  by  5  Babcock  &  Wilcox  boilers,  of  120  horse-power 
each,  the  steam  pressure  at  the  boilers  being  150  Ib.  and  at  the 
engine  145  Ib.  The  consumption  of  coal  is  2.58  Ib.  per  indicated 
horse-power  hour,  which  Mr.  White  considers  very  fair  consider- 
ing the  quality  of  the  coal  and  other  unfavorable  conditions. 

The  ball-mill  is  now  generally  conceded  to  be  an  efficient,  fine 
pulverizer,  and  it  has  the  advantage  of  combining  in  one  apparatus, 
which  is  capable  of  receiving  ore  directly  from  the  breakers  and 
delivering  it  at  the  desired  degree  of  fineness,  the  screening  and 
elevating  mechanism,  which  in  a  roll  plant  have  to  be  provided 
independently.  This  must  necessarily  save  considerable  labor, 
besides  affording  some  other  advantages.  On  the  other  hand, 
the  consumption  of  steel  by  wear  of  the  various  parts  is  un- 
doubtedly very  high  in  the  ball-mills.  The  following  table  shows 
the  wrear  of  the  principal  parts  of  a  No.  5  Krupp  mill  in  pounds 
of  steel  per  ton  of  ore  as  reported  by  Mr.  White: 


TOTAL 

LOSS  1 

N  LBS.  PE 

RTON 

STEEL 

PLATES 

BELTS 

BALLS 

Hunch  plates 

89000 

681 

D  bolts  

4035 

038 

E  bolts  

3039 

023 

Scoop  or  perforated  grinding  plates  

2,814 

.022 

G  bolts. 

321 

002 

Cheek  or  side  grinding  plates 

18900 

144 

Square-headed  bolts  

1  153 

009 

Steel  balls  

94  752 

725 

Total  wear  of  steel  per  ton  crushed 

1  644  Ib 

0  847 

0  072 

0  725 

106 


METALLURGICAL  MILL  CONSTRUCTION 


The  plates  become  useless  when  worn  down  about  two-thirds 
of  their  original  weight.  This  would  reduce  the  actual  wear  of 
metal  in  the  mill  from  0.847  to  0.565  Ib.  per  ton  of  ore,  leaving 
an  apparent  actual  consumption  of  steel  carried  off  in  the  ore  of 
1.362  Ib.  per  ton  of  ore  crushed. 

The  following  table  shows  the  renewal  of  parts  of  16  No.  5 
ball-mills  in  twelve  months,  during  which  time  130,776  long 
tons  of  ore  were  crushed  to  pass  20-mesh  screens,  with  the  cost 
per  ton  for  renewals,  together  with  the  approximate  life  of  some 
of  the  parts: 


NUMBER 
USED  IN 
ONE  NO.  5 
MILL 

NUMBER 
USED   IN 
TWELVE 
MONTHS 

UNIT 

PRICE 
S.      D. 

COST 
PER  TON, 
PENCE 

APPROXI- 
MATE 
LIFE, 
MONTHS 

Steel  balls  

112 

5264 

each 

5  0 

2.412 

Hunch  plates    

40 

1000 

45  0 

4.130 

7i 

Cheek  plates  
Scoop     plates,    perforated 
and  grinding     .  .      ...    . 

20 
10 

270 

80 

ii 

42  4 
80  0 

1.066 
0.587 

14 
18 

Bolts  D 

40 

1153 

n 

1  3 

0  132 

Bolts  E 

40 

1013 

ii 

1  3 

0  115 

Bolts  G 

40 

214 

ii 

1  3 

0.024 

Bolts   square-headed 

60 

769 

ii 

1  3 

0.088 

Fore  sieve  plates,  set  of  five 
Brass  wire  gauze  (set  of  10) 

5 

61 

196 

7876} 

set 

31  6 
0  7* 

0.565 
0.451 

5 
1| 

sq  f  t              ... 

Flannel,  lineal  yds  

644 

1  1 

0.062 

Bag  leather  (sides) 

19 

16  0 

0037 

Clout  nails  (packets) 

183 

0  5 

0  007 

Glass  lubricators 

120 

each 

0  7 

0008 

Set  screws 

227 

Ib 

0  5 

0.008 

Bolts  1$  in.  x  f  in.  . 

269 

0  3 

0.006 

Bolts,  3  in.  x  |  in  

258 

u 

0  3 

0.006 

Bolts,  3  in.  x  £  in  

295 

(t 

0  3 

0.007 

\Vasliers 

752 

« 

0  2 

0  012 

Screen  frames  pine 

10 

108 

0  055 

18 

A  comparison  of  the  results  at  Mount  Morgan  show  operating 
expense  per  ton  of  ore  of  30.330d.,  in  the  case  of  the  ball-mills 
versus  60.28  in  the  case  of  rolls;  maintenance  expense  of  16.777d. 
versus  21.39d.,  a  total  of  47.107d.  versus  81.67d.  It  appears, 
therefore,  that  although  the  consumption  of  steel  in  the  ball- 
mills  was  1.362  Ib.  per  ton  of  ore  crushed,  against  only  0.108  Ib. 
of  roll  shells,  the  cost  of  maintaining  the  ball-mill  plant  was  on 
the  whole  less  than  that  of  the  roll  plant.  With  respect  to  the 
operating  expense,  it  should  be  remarked  that  lid.  occurs  in  the 


ORE-CRUSHING  MACHINERY  107 

item  of  fuel,  which  is  chiefly  due  to  the  more  economical  power 
plant,  while  the  boilers  of  the  roll  plant  supply  some  steam  for 
outside  purposes.  The  fact  that  the  quantity  of  ore  crushed 
per  indicated  horse-power  per  hour  is  substantially  the  same 
in  both  mills  shows  that  the  ball-mills  are  not  really  entitled  to 
the  saving  in  cost  of  power  which  the  Mount  Morgan  figures 
show.  The  advantage  is  chiefly  in  the  item  of  labor  in  running 
expense,  which  is  reduced  18d.,  or  more  than  one-half.  Mr. 
Argall  calls  attention  to  two  other  points,  namely,  that  the  roll 
plant  was  old,  while  its  capacity  was  only  about  one-third  that 
of  the  ball-mill  plant.  The  former  criticism  is  good;  the  latter 
not  so  good,  inasmuch  as  the  roll  plant  was  substantially  the  same 
as  what  he  outlines  as  a  unit  of  maximum  efficiency,  wherefore 
the  reduction  in  cost  per  ton  by  further  increase  in  capacity 
would  probably  be  not  very  important.  The  wages  paid  at 
Mount  Morgan  were  not  stated  by  Mr.  White,  saving  the  single 
remark  that  the  men  attending  the  ball-mills  received  8s.  per 
8-hour  shift,  whence  we  may  infer  the  rates  are  about  the  same 
as  in  Colorado.  It  appears,  however,  that  a  plant  consisting  of 
2  breakers,  2  driers,  and  8  rolls  crushes  only  125  tons  at  Mount 
Morgan,  against  400  tons  in  Colorado.  For  the  coarse  crushing, 
the  Mount  Morgan  plant  has  2  men  at  the  breakers  per  shift  of 
8  hours,  while  the  Colorado  plant  has  2  men  for  a  single  shift  of 
10  hours.  Each  plant  has  1  man  per  8-hour  shift  at  the  driers, 
1  man  at  the  screens,  and  2  men  at  the  rolls  (in  Colorado,  1  man 
" oiling  and  sweeping").  The  elaborateness  with  which  the  sam- 
pling was  done  at  the  Colorado  plant  makes  precise  comparisons 
impossible,  but  it  is  clear  that  the  practical  results  at  Mount 
Morgan  are  inferior.  To  what  extent  this  is  due  to  difference 
in  the  character  of  the  ore,  to  the  lower  efficiency  of  the  crushing 
machinery,  to  the  less  perfect  general  design  of  the  works,  to  the 
less  economical  systemization  of  the  labor,  etc.,  conclusions  can 
hardly  be  drawn  from  the  present  data.  In  the  case  of  the  com- 
parative results  between  the  rolls  and  ball-mills  at  Mount  Morgan, 
however,  the  test  is  valuable  inasmuch  as  the  ore  treated  was 
identical,  although  all  the  conditions  were  not  perhaps  the  same. 
Mr.  Argall  appreciates  the  advantages  which  ball-mills  may  have 
to  those  requiring  small  units,  but  for  large  capacities,  say  from 
GO  tons  per  day  upward,  he  considers  that  rolls  are  vastly  superior. 
It  is  hoped  that  other  engineers  who  are  engaged  in  crushing 


108  METALLURGICAL  MILL  CONSTRUCTION 

ore  on  a  large  scale  will  compile  their  results  under  different 
conditions  with  the  same  minuteness  and  careful  analysis  that 
Mr.  Argall  has  done,  and  thus  throw  further  light  upon  this  im- 
portant subject.  To  him  is  due,  however,  the  thanks  of  the  pro- 
fession for  presenting  scientific  data  whereby  the  capacity  of 
rolls  for  crushing  any  material  to  any  degree  of  fineness  can  be 
computed  with  some  degree  of  accuracy,  and  not  have  to  be  left 
to  guesswork  or  the  rule  of  thumb  deductions  from  imperfect 
experience. 


MODERN  CRUSHING  AND  GRINDING  MACHINERY 

BY  PHILIP  ARGALL 

(May  11,  1904) 

The  recent  discussions  on  fine  crushing  and  grinding  with 
stamps,  pans,  and  tube-mills  appear  to  accentuate  the  principle 
of  crushing  by  "  successive  comminution,"  a  process  that,  with 
others,  I  have  for  many  years  not  only  advocated,  but  also  put 
into  successful  operation. 

The  idea  that  all  the  stages  of  the  process  can  be  carried  out 
by  one  machine,  be  it  roll,  stamp,  or  patent  pulverizer  —  and 
their  name  is  legion  —  appeals  strongly,  both  to  the  uninitiated 
and  the  so-called  practical  man,  "he  who  practices  the  errors  of 
his  predecessors/'  on  account  of  its  apparent  simplicity.  One 
machine  is  to  do  everything,  that  is  to  say,  take  rocks  of  2-in. 
cube  and  crush  them  to  pass  a  screen  aperture  of  say  1-50  in.;  if 
it  amalgamates  at  the  same  time,  so  much  the  better;  and  should 
it  be  able  to  perform  other  functions,  why  that  simply  enhances 
its  value,  although  adding  greatly  to  its  complications.  The 
United  States,  with  more  inventors  to  the  square  mile  than  any 
other  country,  can  lick  creation  on  patent  pulverizers  and  crushers 
that  are  able,  unaided  and  alone,  to  crush  and  grind  coarse  rock 
to  infinite  fineness;  and  the  list  is  being  momentarily  enlarged  by 
well-meaning  farmers,  backwoods  lumbermen,  and  ingenious 
mechanics,  most  of  whom  have  never  seen  a  mine,  and  who 
often  lack  even  the  elementary  knowledge  of  the  practical  re- 
quirements in  ore  reduction.  To  these  inventors  it  is  well  to 
state  clearly  that  the  single  machine  for  fine-grinding  coarse 
rock  is  fast  passing  into  the  friendly  oblivion  such  machines  are 
so  eminently  fitted  to  adorn. 

Those  of  us  who  have  investigated  the  mechanical  efficiency 
of  a  given  machine,  meaning  thereby  the  pounds  of  ore  crushed 
per  horse-power  hour  from,  and  to,  stated  maximum  sizes,  know 
that  each  machine  of  value  has  its  economic  limit,  at  which  it 

109 


110  METALLURGICAL  MILL  CONSTRUCTION 

will  give  the  maximum  output  in  pounds  per  horse-power  hour, 
and  also  that  there  are  fixed  ratios  of  reduction  that  should  not 
be  exceeded.  These  limits,  however,  are  not  in  every  case 
determined,  yet  I  have  no  hesitation  in  stating  that  the  machine 
which  reduces  a  2-in.  cube  to  pass  a  1-50-in.  screen-aperture,  in 
one  operation,  is  a  very  inefficient  apparatus,  even  if  it  should 
prove  to  be  the  most  modern  1350-lb.  stamp. 

I  have  elsewhere  shown  that  the  efficiency  of  a  rock-breaker 
falls  off  rapidly  when  a  reduction  exceeding  4  to  1  is  attempted, 
say  8-in.  to  2-in.  cubes,  and  the  same  rule  holds  good  for  rolls;  and 
that  for  reducing  ores  below  two  inches,  rolls  are  vastly  superior 
to  rock-breakers,  for  the  reason  that,  while  both  machines  work 
practically  on  the  same  principle,  one  is  an  unbalanced,  or,  at 
best,  imperfectly  balanced,  intermittent-action,  reciprocating 
machine,  and  the  other  a  perfectly  balanced,  continuous-action 
rotary  machine.  Large  rolls  could  be  constructed  that  would 
compete  favorably  with  rock-breakers  on  sizes  above  two  inches, 
but  they  would  be  heavy,  cumbersome,  and  difficult  to  trans- 
port to  the  metal-mining  regions,  so  I  hold  that  the  combina- 
tion of  breakers  and  rolls  I  have  indicated  best  answers  our 
present  requirements  in  metal  mines,  where  the  rock  going  to  the 
breakers  is  never  of  unusual  size  —  as  quarry  rock,  for  ex- 
ample.1 

The  reason  that  a  4  to  1  reduction  should  not  be  exceeded  in 
rock-breakers  is  obvious  to  any  one,  and  to  a  great  extent  the 
same  rule  applies  to  rolls.  The  economic  limit  of  rolls,  crushing 
dry,  is  from  2  in.  to  about  0.02-in.;  below  this  their  efficiency 
falls  off.  With  average  quartzose  ores  I  have  reduced  with  four 
rolls  in  series  330  Ib.  per  horse-power  hour  from  0.75  to  0.02-in., 
crushing  dry,  and  I  believe  practically  as  high  an  efficiency  can 
be  attained  in  wet  crushing  with  a  properly  designed  roll. 

Now,  it  may  be  asked,  what  is  the  economic  range  of  stamps? 
Some  say,  it  matters  not  whether  the  ore  is  fed  in  pieces  up  to 
cubes  of  2-in.  maximum,  or  in  cubes  as  small  as  J-in.,  the  capacity 
through  a  given  screen-aperture  will,  in  either  case,  be  the  same; 
while  others  claim  a  larger  output  for  the  i~in.  feed;  good  men 
can  be  found  supporting  either  side  of  the  argument.  Now,  I 

i  The  Edison  giant  rolls  are  employed  in  some  large  mills,  among^  them 
the  mill  of  the  New  Jersey  Zinc  Company  at  Franklin  Furnace,  N.  J.,  instead 
of  rock-breakers.  —  EDITOR. 


ORE-CRUSHING  MACHINERY  111 

hold  that  recent  practice  has  quite  wrongly  placed  on  the  stamp 
much  of  the  work  that  can  be  better  performed  by  breakers  and 
rolls,  and  this  error  has  been  intensified  by  constantly  increasing 
the  weight  of  the  stamp,  so  that  it  can  smash  any  size  of  rock 
that  enters  the  mortar.  Passing  to  the  other  extreme,  the  stamp 
is  not  an  efficient  fine-crushing  machine  —  never  was,  nor  from 
its  construction  can  it  ever  be.  It  is  just  possible  that  a  1250-lb. 
stamp  might  sink  through  a  J-in.  bed  and  even  strike  the  die, 
and  so  a  well-prepared  ore  might,  under  these  conditions,  show 
even  a  lower  stamp-efficiency  than  if  the  batteries  were  fed  with 
a  maximum  cube  of  two  inches,  as  in  the  latter  case  there  would  be 
material  on  the  die  that  would  resist  the  weight  of  the  falling 
stamp,  to  the  end  that  the  greater  part  of  the  energy  would  be 
expended  in  the  useful  work  of  crushing  ore.  Supposing,  how- 
ever, that  £-in.  cubes  are  fed  to,  let  us  say,  an  800-lb.  stamp, 
and  the  output  from  the  latter  stamp  was  fully  as  great  as  that 
of  the  heavier  one  (as  in  most  cases  I  know  it  would  be) ,  then  the 
stamp  advocates  would  be  compelled  to  admit  there  was  some- 
thing wrong.  So  it  becomes  necessary  to  reason  out  whether 
stamps  or  rolls  are  the  more  efficient  machine  for  reducing  ores 
from  2-in.  to  J-in.  cubes,  and  to  this  there  can  be  but  one  answer, 
as  all  must  admit  the  stamp  is  not  a  coarse  crusher;  we  have 
previously  seen  that  it  is  not  a  fine  crusher.  Hence,  if  it  has  an 
economic  range  comparable  with  modern  machines,  it  must  be 
somewhere  between  ^  in.  and  1-50  in.,  and  even  within  this 
range  I  maintain  rolls  are  more  efficient,  even  if  the  stamps  are 
used  in  series  in  order  to  secure  in  their  operation  the  benefits  of 
''successive  comminution." 

The  trouble  with  stamps  —  apart  from  their  being  recipro- 
cating machines  in  which  a  dead  weight  of  1000  to  1350  Ib.  has 
to  be  picked  up  from  a  state  of  rest  by  a  rapidly  rotating  cam 
100  times  per  minute  —  is  that  modern  practice  attempts  to  do 
too  much  with  them;  crushing  ore  from  2  to  0.02  in.  is  a  reduction 
of  100  to  1,  against  say  4  to  1,  for  other  classes  of  crushing  ma- 
chines. Surely  this  enormous  range  of  reduction  cannot  be  sound 
practice.  Therefore,  I  hold,  the  modern  practice  of  increasing 
the  weight  and  range  of  reduction  of  the  stamp  is  all  in  the  wrong 
direction,  and  that  in  attempting  to  do  the  work  of  rock-breakers 
or  rolls  with  a  stamp,  no  matter  what  its  weight,  the  results  will 
invariably  be  a  much  more  expensive  plant,  and  one  of  greatly 


1 1 2  METALLURGICAL  MILL  CONSTRUCTION 

impaired  efficiency,  as  measured  by  the  weight  of  rock  crushed 
per  horse-power  hour. 

To  lift  1250  Ib.  to  crush  a  2-in.  cube  of  hard  rock  may  be 
defended,  but  to  use  the  same  weight  on,  say,  0.08  and  0.04-in. 
particles,  to  reduce  them  to  pass  a  1-50-in  screen-aperture,  does 
not  appeal  to  any  sense  of  fitness.  This  brings  up  another  point : 
large  pieces  of  rock  yield  best  to  a  crushing  force,  smaller  ones 
to  grinding,  and  while  there  is  some  grinding  action  between  the 
large  and  fine  rock  in  a  stamp-mortar,  it  is  on  the  whole  insig- 
nificant, and  for  this  reason  pans  and  tube-mills  are  vastly  more 
efficient  for  reducing  sands  and  fine  ore  than  stamps  or  any 
other  form  of  crushing  or  impact  machines. 

I  do  not  desire  to  establish  any  set  figures  regarding  the 
weight  of  stamps  or  the  fineness  of  the  ore  fed  to  them;  such 
factors  will  depend  somewhat  on  the  nature  of  the  ores  treated 
in  any  given  case,  and  can  be  worked  out  by  those  in  charge  of 
stamp-mills. 

The  accompanying  diagram  shows  the  efficiency  in  pounds 
per  horse-power  hour  of  stamps  and  rolls  crushing  from  about 
2  in.  to  1-50  in.  maximum.  I  would  point  out,  however,  that  the 
stamp  will  give  a  greater  proportion  of  fine  material;  in  other 
words,  in  discharging  through  the  same  size  screen-aperture  the 
stamp  will  crush  from  10  to  15  per  cent,  finer  than  the  roll  — 
used  as  a  wet  crusher  —  and  this  must  be  allowed  for,  as  useful 
work  done. 

My  idea  of  a  roll  plant  to  reduce  ores,  dry,  from  2  in.  to  1-50  in. 
would  be  as  follows: 

Rough  rolls from    2    to  0.75  in. 

Second    "    "    0.75  "  0.24  " 

Third      "   "    0.24  "  0.08  " 

Fourth    "   "    0.08  "  0.02  " 

Taking  a  crushing  and  amalgamating  plant  in  which  the  ore 
is  finally  reduced  to  1-400  in.  for  filter-press  work,  I  would  suggest 
the  following  as  the  best  and  most  economical  arrangement: 

Rock-breakers to  2.00  in. 

Rolls  in  series  crushing  wet "  0.06  " 

Grinding  and  amalgamating  pans "  0.02  " 

Tube-mills to  infinity. 


ORE-CRUSHING  MACHINERY 


113 


•  101 

•.10  rr 



-L 

15 

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0 

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200 

—  1--I-4-  Mill 

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50                          SO 

1  1  1  1  1  1  1  1  iT01*' 

_  .     . 

T        1      MM          1       1      1       i  1  1  1.  1 
Stamp  and  Roll 

Capacity 

T 

| 

In  Pounds  per  H.P.H. 

• 

Feed  1.5  to  2  maximum 
Quartz  Ore 

.  .  ]__ 

v 

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lip  Argall 

Denver,  Colo. 

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ISOLbs.  8COLbs.  260  Lbg.  800  Lbe. 

^    Per  Horse  Power  Hour 

FIG.  16. 


114  METALLURGICAL  MILL  CONSTRUCTION 

The  pan-mill  might  be  depended  upon  to  catch  most  of  the 
amalgamable  gold;  plates  would  be  required  only  after  the  tube- 
mill,  to  catch  such  gold  as  had  been  liberated  by  the  finer  grinding. 
I  can  even  conceive  of  such  an  arrangement  of  plant  for  amalga- 
mation only.  Stopping  the  tube-mill  work  at  such  a  degree  of 
fineness  as  gave  the  best  results  —  call  it  for  argument  1-100  in. 
—  and  it  can  be  demonstrated  that  with  such  a  plant  ore  can  be 
reduced  to  1-100  in.  cheaper  than  by  stamps  to  1-50  in.  in  the 
best  modern  mills. 

Finally,  the  stamp,  if  it  survives  in  modern  ore-reduction 
plants,  will  be  only  one  unit  in  a  series  of  machines,  with  its 
range  of  reduction  restricted  within  very  narrow  limits. 


SPRINGS  ON  CRUSHING  ROLLS 

BY  LEWIS  SEARING 

(April  6,  1905) 

Most  machinery  peculiar  to  any  one  industry  is  the  result  of 
an  evolutionary  process  involving  experiment  and  the  test  of 
time;  nevertheless,  some  useless  and  complicated  feature  of  de- 
sign may  remain,  simply  because  its  existence  has  never  been 
questioned.  Such  machines  are  designed  according  to  tradition 
and  custom,  without  reference  to  the  particular  necessity  of 
each  case.  The  use  of  springs  on  the  so-called  modern  ore- 
crushing  rolls  is,  in  my  opinion,  one  of  the  useless  features  of 
design  which  has  not  heretofore  been  questioned. 

The  use  of  the  springs  is  a  provision  for  but  one  condition  of 
operation  —  the  presence  of  foreign  uncrushable  material  in  the 
ore.  There  can  be  no  doubt  that  sudden  strain  is  developed  in 
the  rolls  when  a  hammer-head,  or  similar  article,  is  caught  be- 
tween the  shells;  but  whether  the  springs  are  absolutely  necessary 
to  prevent  serious  damage  under  this  condition  is  a  point  seldom 
considered  by  the  mill  superintendent;  rather,  he  takes  it  for 
granted  that  they  are  necessary;  indeed,  it  has  been  well  said 
that  the  use  of  springs  is  a  habit  established  by  estimated,  rather 
than  actual,  necessity. 

The  disadvantages  of  the  spring  rolls  are  twofold.  In  the 
first  place,  a  set  of  good  spring  rolls  is  costly  in  design  and  in 
manufacture;  15  to  20  per  cent,  of  the  cost  can  be  traced  directly 
to  the  springs  and  their  attendant  mechanism.  In  the  second 
place,  any  neglect  of  the  spring  tension  will  result  in  an  undue 
proportion  of  oversized  product.  Who  can  say  that  it  is  possible 
to  secure  an  adjustment  of  the  springs  which  will  produce  an 
even  product  and  at  the  same  time  permit  of  sufficient  flexibility 
for  the  passage  of  a  hammer-head  without  throwing  the  driving- 
belt? 

The  absolute  prevention  of  an  oversize  product  is  greatly  to 

115 


116  METALLURGICAL  MILL  CONSTRUCTION 

be  desired  when  such  a  result  can  be  obtained,  and  this  is  possible 
by  the  use  of  rigid  rolls.  It  materially  reduces  the  time  and  cost 
of  crushing,  and  also  eliminates  one  elevator  and  its  accessories, 
and  permits  a  reduction  in  either  the  size  or  the  number  of  rolls 
to  be  installed. 

A  minor  point,  worthy  of  consideration,  is  the  pounding, 
jarring,  and  vibration  accompanying  the  operation  of  spring  rolls 

—  hard   upon  the  building   and  attendants   alike  —  but   which 
is  entirely  obviated  by  the  use  of  rigid  rolls. 

It  is  well  known  to  mechanical  engineers  that  the  shock  and 
strain  on  rolls  employed  in  the  manufacture  of  steel  rails  is  ter- 
rific, especially  when  the  steel  billet  is  introduced  to  the  first,  or 
breaking-down,  set  of  rolls.  It  requires  an  enormous  amount  of 
power  to  reduce  the  thickness  of  the  metal  a  fraction  of  an  inch 

—  enough,  in  fact,  to  produce  a  perceptible  momentary  reduction 
in  the  speed  of  the  huge  engines  employed,  the  change  from  no 
load  to  full  load  being  instantaneous.     Again,  the  tremendous 
variation  of  load  on  steam  shovels,  dredges,  and  similar  machines 
is  a  matter  of  common  knowledge.     There  is  also  the  case  of  the 
ore-crusher.     Notwithstanding   the   strain   and  shock  to   which 
this  type  of  machinery  is  subjected,  no  springs  are  involved  in 
the  mechanism,  and  the  design  shows  all  parts  fixed  and  rigid 
throughout. 

Now,  if  the  complications  attendant  upon  the  use  of  springs 
are  avoided  in  steel  rolling-mills,  steam  shovels,  and  dredges, 
and  the  various  forms  of  ore-crushers,  why  is  it  not  reasonable 
to  affirm  that  these  complications  can  also  be  avoided  in  the 
construction  of  crushing  rolls,  which,  it  must  be  allowed,  have 
comparatively  easy  duty?  If  these  other  machines  can  be  made 
to  operate  successfully  under  far  more  severe  duty,  then  ore- 
crushing  rolls  involving  the  same  principle  of  design  will  also 
operate  successfully. 

Even  if  there  were  no  difference  in  the  first  cost,  and  the  entire 
extra  cost  of  the  spring  mechanism  were  devoted  to  strengthening 
the  bearings  and  frame  of  rigid  rolls,  the  simplification  of  the 
machine  and  the  prevention  of  oversized  product  would  be 
accomplished.  As  a  matter  of  fact,  rigid  rolls  are  now  being 
manufactured  and  sold  at  appreciably  lower  prices  than  spring 
jolls  of  the  same  size.  If  rigid  rolls  be  properly  designed  it  is 
impossible  for  the  belt  to  transmit  sufficient  power  to  injure  the 


ORE-CRUSHING  MACHINERY  117 

rolls;  but,  as  a  precaution,  a  safety  device,  such  as  a  wooden, 
instead  of  a  metal,  key  in  the  driving  pulleys  may  be  used.  In 
the  event  of  complete  stoppage,  this  key  will  sheer,  or  the  belt 
will  slip,  before  the  rolls  can  be  injured. 

It  may  be  argued  that  rigid  rolls  would  be  acceptable  were  it 
not  necessary  to  provide  an  adjustment  to  compensate  for  wear. 
This,  however,  is  a  simple  matter  and  as  easily  arranged  as  the 
adjustment  necessary  on  the  rolls  in  the  steel  mill. 

Finally,  in  view  of  the  fact  that  rigid  rolls  have  been  in  suc- 
cessful operation  at  the  plants  of  the  Osceola  Copper  Company, 
at  Houghton,  Michigan,  and  the  North  American  Lead  Company, 
at  Fredericktown,  Missouri,  it  would  seem  a  safe  prediction  to 
say  that  the  use  of  springs  on  crushing  rolls  will  soon  become  a 
matter  of  interesting  mechanical  history. 


NOTES  ON  SOME  REGRINDING  MACHINES 

BY  MARTIN  SCHWERIN 

(March  10,  1904) 

Two  years  ago  I  made  a  series  of  tests  on  four  types  of  re- 
grinding  machines  in  the  old  concentrator  of  the  Anaconda 
Copper  Mining  Company,  at  Anaconda,  Montana.  The  results 
of  these,  together  with  some  observations,  are  here  given  in  the 
belief  that  the  interest  in  this  feature  of  ore-dressing  is  unabated. 
That  the  difficulties  and  complexities  have  not  diminished  is 
attested  by  the  divergence  of  opinions  held  by  recent  writers. 

In  any  comparison  of  fine  grinding  machines  and  reports  of 
work  accomplished  by  them  the  condition  of  the  ore  fed  into  them 
is  recognized  to  have  a  significant  effect.  It  is  evident  that  the 
condition  of  the  ore  —  whether  it  is  fine  or  coarse  —  not  only 
affects  the  capacity  and  character  of  work  done,  but  even  when 
these  conditions  are  the  same  for  all,  various  machines  are  affected 
differently  by  changes  in  the  conditions. 

In  the  published  reports  of  ball-mills  working  a  coarse  material 
from  a  Blake  or  Gates  crusher  and  discharging  it  in  a  finely 
comminuted  condition,  it  appears  that  the  machine  is  well 
adapted  to  the  work.  It  is  a  most  efficient  screening  machine, 
and  on  this  account  it  is  better  adapted  to  a  preliminary  reduction 
of  ore  in  preparing  it  for  a  first  metallurgical  treatment,  than  it 
is  for  regrinding  particles  that  are  already  reduced  to  a  size 
approaching  that  desired  in  the  discharge  of  the  machine;  more 
concisely,  it  is  better  adapted  to  grinding  between  very  wide 
size-limits  than  it  is  for  regrinding  between  very  close  size-limits. 

In  the  latter  case  it  frequently  happens  that  as  much  as  from 
50  to  75  per  cent,  of  the  feed  is  already  smaller  than  the  width  of 
slot  or  free  aperture  of  the  screen-cloth  used  in  the  machine. 
This  was  the  case  at  Anaconda,  where  the  feed  was  wet  jig-tailings. 
The  result,  in  this  use  of  the  ball-mill,  was  a  rapid  screening  out 
of  the  under-size  feed  with  scarcely  any  grinding.  It  may  be 

118 


ORE-CRUSHING  MACHINERY  119 

suggested  that  the  remedy  is  the  use  of  a  finer  screen  in  the 
ball-mill;  but  this  is  not  the  remedy.  Practical  considerations 
and  the  necessity  for  discharging  a  jigable  product  control  the 
size  of  the  screen  and  do  not  allow  the  use  of  one  with  much  less 
than  1 .5  mm.  slots.  It  is  absolutely  essential  that  any  successful 
regrinding  machine  should  be  able  to  work  effectively  between 
close  size-limits. 

In  the  appended  tabulated  results  it  is  seen  that  the  screening 
ability  of  the  ball-mill  and  the  deterioration  in  effective  crushing 
increase  alarmingly  with  the  life  of  the  lining  and  screens.  This 
is  partly  due  to  the  enlargement  of  the  holes  in  the  armor-plate 
and  partly  to  the  wear  of  the  screens.  From  a  diameter  at  the 
small  end  of  the  holes  in  the  armor-plate  of  -f$  in.  they  wore  in 
five  months  to  J-  in.  The  increased  size  afforded  greater  facility 
for  the  particles  of  ore  to  pass  through  to  the  outer  screens, 
thereby  escaping  the  action  of  the  balls.  While  a  granular  product 
is  desirable,  it  must  not  be  attained  at  the  sacrifice  of  effective 
grinding. 

The  tailings  from  jigs  handling  the  ball-mill  product  for  a 
period  of  ten  days,  during  which  they  were  systematically  sam- 
pled, averaged  0.925  per  cent,  copper.  During  the  same  period 
the  tailings  from  jigs  treating  the  product  from  Chilean  mills 
averaged  0.595  per  cent,  copper.  The  feed  of  both  machines  was 
nearly  the  same  in  copper  value.  During  the  same  period  the 
tailings  from  the  first  tail-sieve  of  the  ball-mill  jigs  (treating  the 
coarsest  of  four  sizes  made  by  the  hydraulic  classifier)  assayed 
1.3  per  cent,  copper. 

Such  results  are  to  be  expected  from  an  inspection  of  the 
asasys  on  the  sized  products  of  the  two  machines.  From  these 
we  see  how  much  richer  in  proportion  to  the  assay  of  the  unsized 
feed  are  the  coarse  sizes  discharged  by  the  ball-mill  compared  to 
the  coarse  sizes  discharged  by  the  Chilean  mill.  Bearing  in  mind 
that  the  feed  is  tailings  and  therefore  contains  very  little,  if  any, 
free  mineral  in  the  coarse  sizes,  it  is  evident  that  the  high  assay 
of  those  sizes  from  the  ball-mill  is  a  consequence  of  the  failure  of 
the  machine  to  grind  them.  These  particles  leave  the  machine 
containing  the  locked-in  mineral,  to  free  which  was  the  object  of 
regrinding.  That  such  enclosed  mineral  goes  into  the  fine  sizes 
when  released  is  shown  by  an  inspection  of  the  assays  of  the 
material  discharged  by  the  Chilean  mill.  It  is  evident  that  the 


120  METALLURGICAL  MILL  CONSTRUCTION 

ball-mill  is  not  adapted  to  regrinding  tailings  for  further  concen- 
tration. 

Another  serious  objection  to  it  is  that  it  requires  most  careful 
feed  regulation  when  running  anywhere  near  its  capacity.  When 
the  feed  becomes  heavier  than  the  machine  can  handle  and  con- 
tinues so  for  a  while,  it  packs  solidly  between  the  screens  and  the 
armor-plate,  and  it  becomes  necessary  to  shut  down,  remove  the 
outside  screens,  and  then  rotate  the  mill  to  free  it.  Without 
shutting  down,  certain  hours  of  running  become  necessary,  with 
all  feed  shut  off,  to  get  the  machine  free  again.  This  is  one  of  the 
practical  considerations,  before  mentioned,  which  control  the 
size  of  the  screens.  But  this  objection,  like  the  others,  has  not 
the  same  application  when  crushing  large  pieces  to  a  small  size, 
because  in  this  latter  case  the  screening  capacity  is  so  greatly  in 
excess  of  its  grinding  capacity  that  no  congestion  of  the  screens 
can  occur  through  the  mere  mass  of  material  forced  against  them. 

The  absence  of  the  dull  roar  characteristic  of  the  ball-mill 
when  running  properly  gives  warning  of  the  danger  from  over- 
feeding. But  the  world  over  the  "graveyard  shift"  in  a  mill  is 
notoriously  heedless  of  all  such  warnings. 

The  size  of  the  Krupp  ball-mill  was  that  measuring  10  ft.  10  in. 
in  hight  by  15  ft.  6  in.  in  breadth  over  all,  with  drum  4  ft.  6  in. 
by  9  ft.  diameter. 

The  Chilean  mill  tested  was  an  original  Bradley  mill,  in  which 
certain  improvements  were  made  at  the  foundry  of  the  Anaconda 
Copper  Mining  Company,  under  the  direction  of  Messrs.  Evans 
and  Waddel.  The  improvements  consisted  principally  of  a  spider 
with  rigid  arms  on  which  the  rollers  were  hung  in  the  place  of 
the  three-socket  jointed  trunnions. 

This  mill  is  well  adapted  to  regrinding  lean  tailings  and 
poorly  suited  for  comparatively  rich  tailings  or  middlings.  Lean 
tailings  from  copper  concentrating  contain  but  a  small  quantity 
of  sulphides  very  thoroughly  distributed  through  the  quartz 
grains  as  minute  enclosed  particles.  It  is  necessary,  in  order  to 
liberate  the  sulphides,  that  the  whole  of  the  feed  be  very  finely 
pulverized.  And  in  doing  this,  if  the  process  be  not  carried  too 
far,  there  is  but  slight  danger  of  the  liberated  mineral  particles 
being  ground  a  second  time,  thereby  unduly  sliming  them,  because 
of  the  protection  afforded  by  the  larger,  harder,  and  more  resistant 
grains  of  quartz.  Such  material  is  the  tailings  from  jigs  after 


ORE-CRUSHING  MACHINERY  121 

fine  rolls.  It  will  usually  be  found  more  profitable  to  regrind 
the  middlings  from  such  jigs  in  the  same  set  of  rolls  or  in  a  Hunt- 
ington  mill. 

The  action  most  desirable  on  such  middlings  is  to  have  each 
grain  cracked  open  once  and  then  freed.  Rolls  do  this  almost 
perfectly,  provided  the  grains  are  not  too  small  for  effective 
work.  Huntington  mills  do  it  less  perfectly,  but  are  capable  of 
doing  effective  work  on  very  much  smaller  grains.  This  action 
would  not  be  sufficient  for  the  poor  tailings.  On  them  the 
cracking  or  grinding  must  be  repeated.  The  sizing  assays  show 
how  well  the  Chilean  mill  does  this.  But  this  very  desideratum 
for  the  tailings,  if  carried  out  on  middlings  would  be  disastrous 
on  account  of  the  larger  size  of  the  enclosed  sulphide  particles  in 
proportion  to  the  size  of  the  enclosing  grains  of  gangue. 

The  Chilean  mill  has  a  large  capacity,  which  is  a  very  necessary 
adjunct  of  any  machine  put  to  regrinding  tailings.  Since  the 
tenor  in  copper  of  the  first  wasted  tailings  is  influenced  no  less 
by  the  proportion  cut  out  for  regrinding  than  by  the  character 
of  the  regrinding  itself,  the  greater  the  proportion  reground, 
the  poorer  will  be  those  tailings  sent  to  the  dump. 

This  machine  is  not  sensitive  to  varying  loads.  If  over-  or 
under-loaded  it  does  its  work  without  serious  impairment  of 
efficiency. 

The  size  of  the  screens  is  the  principal  factor  in  the  capacity 
of  the  Chilean  mill  and  may  even  be  said  to  control  it.  Being 
on  the  outside,  they  are  perfectly  accessible,  as  they  are  in  a 
stamp-mill,  and  the  condition  in  which  they  are  kept  by  the 
attendant  is  of  great  importance  if  the  full  duty  is  to  be  main- 
tained. The  output  will  be  almost  proportional  to  the  ratio 
between  the  number  of  blinded  holes  to  the  total  number  of 
holes.  But  if  the  duty  of  the  machine  be  light,  a  regulation  of 
the  character  of  the  discharged  product  can  be  exercised  through 
the  condition  of  the  screens.  By  keeping  a  large  proportion  of 
holes  blinded  all  the  time  almost  any  degree  of  pulverization  can 
be  attained.  The  same  end,  however,  can  be  accomplished  better 
and  more  directly  by  the  use  of  finer  screens. 

Attention  is  called  to  the  results  of  the  experiment  designed 
to  show  the  variations  in  the  product  corresponding  to  varia- 
tions in  the  load.  The  first  column  is  not  important,  but  it 
is  given  to  show  that  there  were  differences  in  the  assays  of 


122 


METALLURGICAL  MILL  CONSTRUCTION 


VARIATIONS  IN  CHILEAN  MILL  PRODUCT  CORRESPONDING  TO 
VARIATIONS  IN  LOAD 


COPPER  ASSAY 
OF  UNSIZED 
SAMPLE 
% 

TONS  PER  HOUR 

SIZE 

WEIGHT 

% 

COPPER 
ASSAY 

% 

DISTRIBU- 
TION OF 
COPPER 
% 

1.49 

2.2 

over  20  mesh 

9.3 

.96 

5.9 

«     40     « 

32.0 

.91 

19.6 

"     80     " 

20.0 

1.15 

15.3 

thr.  80     " 

38.5 

2.30 

59.4 

1.37 

2.3 

over  20  mesh 

7.5 

.87 

4.7 

"     40     " 

30.3 

.78 

17.2 

"     80     " 

22.8 

1.00 

16.6 

thr.  80     " 

39.4 

2.15 

61.5 

1.30 

4.0 

over  20  mesh 

7.7 

.91 

5.4 

"     40     " 

38.8 

.86 

25.7 

"     80     " 

20.0 

1.04 

16.0 

thr.  80     " 

33.3 

2.08 

52.9 

1.39 

5.0 

over  20  mesh 

13.5 

.75 

7.3 

"     40     " 

37.1 

.85 

22.7 

"     80     " 

19.1 

1.09 

14.9 

thr.  80     " 

30.3 

2.54 

55.1 

1.71 

6.0 

over  20  mesh 

18.7 

.83 

9.0 

"40     " 

31.8 

.97 

18.0 

"     80     " 

19.7 

1.74 

20.0 

thr.  80     " 

29.7 

3.05 

53.0 

1.58 

6.6 

over  20  mesh 

18.8 

.88 

10.5 

"     40     " 

35.7 

1.12 

25.3 

"     80     " 

19.6 

1.52 

18.7 

thr.  80     " 

25.9 

2.78 

45.5 

1.48 

7.25 

over  20  mesh 

28.1 

.95 

18.0 

"     40     " 

30.2 

1.07 

21.8 

"     80     " 

16.6 

1.40 

16.4 

thr.  80     " 

25.0 

2.65 

43.8 

1.48 

8.16 

over  20  mesh 

26.3 

.75 

13.3 

"     40     " 

34.8 

1.08 

25.3 

"     80     " 

19.0 

1.66 

21.3 

thr.  80     " 

20.0 

2.96 

40.1 

HUNTING-TON  MILL  PRODUCT 

AVERAGE  OF  6  SAMPLES 


1.48 


1.98 


Over  20  mesh 

12.7 

.82 

7.0 

"     40     " 

43.5 

.92 

27.0 

"     80     " 

17.8 

1.52 

18.1 

"  160     " 

10.9 

2.07 

15.2 

thr.  160     " 

15.0 

3.22 

32.6 

KRUPP  MILL  PRODUCT 

AVERAGE  OF  5  SAMPLES   (DURING    ISt  MONTH'S  RUN) 

Over  10  mesh 

3.4 

1.60 

2.7 

"     20     " 

20.3 

1.65 

16.9 

"     40     " 

37.6 

1.54 

29.2 

"     80     " 

15.3 

1.83 

14.1 

"  160     " 

13.5 

2.70 

18.4 

thr.  160     " 

11.4 

3.21 

18.4 

ORE-CRUSHING  MACHINERY 


123 


KRUPP  MILL  PRODUCT 

AVERAGE  OF  4  SAMPLES  (DURING  6  MONTHS'  RUN) 


1.4 


Over  10  mesh 

23.7 

1.41 

22.9 

"  20 

31.7 

1.35 

29.3 

"  40 

29.5 

1.28 

25.8 

"  80 

5.5 

1.52 

5.7 

"  160 

4.4 

2.16 

6.5 

thr.  160 

4.4 

3.36 

10.1 

GATES  ROLL  PRODUCT 

AVERAGE  OF  4  SAMPLES 


Over  10  mesh 

14.2 

"  20 

30.2 

"  40 

29.6 

"  80 

12.2 

"  160 

5.8 

thr.  160 

7.3 

SUMMARY 


KRUPP  BALL- 
MILL  NO.  8 

HUNTINGTON 
MILL 

CHILEAN  MILL 

GATES  ROLLS 

Capacity  in  tons 
per  hour 

5.0 

3.0 

6.0 

9.0 

Screens  used 
(mm.) 

1.5 

1.5 

1.5 

1.5 

Speed  r.p.m. 

21 

65 

34 

108 

Size  of  machine 

DRUM  4  FT.  6  IN. 
BY  6  FT.  DIAM. 

DIE  RING  5  FT. 
DIAM. 

DIE  RING  6  FT. 
DIAM. 

SHELLS  15  IN. 
FACE  BY  36  IN. 
DIAM. 

the  feed.  Such  differences  were  unsought  and  undesirable, 
but  were  unavoidable.  From  the  table  it  is  seen  that,  as  the 
tons  per  hour  increase,  the  discharge  contains  greater  per- 
centages of  coarse  sizes  and  smaller  percentages  of  fine  sizes. 
This  is  explained  when  it  is  remembered  that  the  greater  the 
quantity  of  material  in  the  machine  the  greater  is  the  amount 
that  is  dashed  against  the  screens  at  each  revolution  of  the 
rollers  and  scrapers,  affording  opportunity  for  greater  num- 
bers of  particles  to  escape  without  grinding  or  with  less 
grinding,  while  the  amount  of  material  that  is  actually  ground 
between  the  rollers  and  die-ring  is  not  increased.  Also,  since 
there  can  be  no  accumulation  of  feed  beyond  a  certain  point,  soon 
reached,  the  greater  the  amount  fed  into  the  machine  the  shorter 
is  the  time  a  given  particle  can  stay  in  it. 

In  the  last  column  are  shown  the  relative  amounts  of  copper 


124  METALLURGICAL  MILL  CONSTRUCTION 

in  the  several  sizes.  The  lower  tonnages,  accompanied  by  more 
perfect  grinding,  are  also  characterized  by  less  copper  in  the 
coarse  size.  This  column  shows  how  the  slimes  run  up  in  copper 
as  the  burden  on  the  machine  diminishes,  and  how  the  coarse 
sizes  carry  more  as  the  burden  increases.  These  effects  are 
apparent  when  the  extreme  sizes  are  used  as  criteria.  No  infor- 
mation is  furnished,  apparently,  by  the  intermediate  sizes  with 
respect  to  variations  in  weight  percentages,  but  the  copper  assays 
on  these  sizes  indicate  that  they  are  leaner  when  the  amount  of 
feed  is  small  and  richer  when  the  amount  of  feed  is  large. 

The  more  copper  in  the  coarse  sizes  (using  the  last  column  as 
the  criterion)  the  less  favorable  is  the  product  for  concentration, 
bearing  in  mind,  of  course,  that  these  are  lean  tailings  in  which 
nearly  all  of  the  copper  minerals  are  in  very  fine  particles  imbedded 
in  gangue  from  which  a  concentrate  of  the  coarser  sizes  cannot 
be  made.  The  results  are  believed  to  substantiate  the  statement 
that  the  Chilean  mill  finds  its  proper  place  in  regrinding  the 
leanest  practicable  tailings.  If  the  feed  were  richer  and  the  indi- 
vidual sulphide  particles  larger,  the  effect  of  sliming  would 
become  prejudicial. 

Some  further  elucidation  becomes  necessary  to  a  complete 
understanding  of  the  sizing  assays.  Although  the  facts  stick  out 
plainly  enough,  the  reason  is  not  at  once  manifest  why  the  same 
coarse  size  in  the  products  of  different  machines  shows  so  great 
a  difference  in  copper  contents,  even  after  making  any  correction 
that  may  be  thought  proper  on  account  of  the  initial  assay  differ- 
ences between  one  unsized  discharge  and  another.  The  mere 
fact  that  in  the  ball-mill  discharge  there  is  a  much  larger  percent- 
age of  the  size  designated  as  over  20-mesh  than  in  the  Chilean 
mill  product  is  not  of  itself  good  reason  why  it  also  assays  higher. 
The  like  sizes  in  the  two  products  contain  unlike  material.  In 
the  case  of  the  ball-mill  the  size  under  discussion  contains  nearly 
the  identical  grains  of  that  size  which  came  in  with  the  feed, 
while  in  the  case  of  the  Chilean  mill  product  the  same  size  con- 
tains a  greater  proportion  of  grains  newly  made  from  the  breaking 
up  of  larger  grains  in  the  machine.  And  so  with  the  next  smaller 
size  to  a  less  extent.  When  a  large  grain  is  broken  it  is  approxi- 
mately true  that  the  sulphides  find  their  place  way  down  the  table 
of  sizes,  while  the  quartzose  material  stays  nearly  where  it  was 
in  the  scale.  The  grains  consisting  partly  of  sulphides  and  partly 


ORE-CRUSHING  MACHINERY  125 

of  gangue  take  intermediate  positions  corresponding  to  the 
predominating  component  mineral. 

The  Huntington  mill  tested  was  one  of  the  under-driven, 
geared,  5-ft.  size,  and  was  run  at  65  revolutions  per  minute. 
The  product  made  is  seen  to  be  similar  to  that  of  the  Chilean 
mill  when  handling  about  6.5  tons  per  hour.  From  this  it  must 
not  be  inferred  that  the  results  would  be  so  nearly  alike  on  material 
a  great  deal  richer,  such  as  middlings  might  be.  On  the  richer 
feed  the  Huntington  mill  results  would  not  change  greatly  with 
respect  to  distribution  of  copper,  while  the  Chilean  mill  product 
would  correspond,  with  respect  to  copper  distribution,  more 
nearly  to  the  results  shown  for  a  burden  of  2  tons  per  hour, 
which,  although  an  actual  necessity  on  the  low-grade  tailings, 
would  be  unnecessary  and  highly  undesirable  on  rich  stuff  because 
the  slime  losses  would  be  excessive  in  the  subsequent  operations. 
On  such  stuff,  therefore,  the  Huntington  mill  shows  to  great 
advantage. 

With  this  mill,  as  with  the  Chilean  mill,  screens  of  any  desired 
degree  of  fineness  can  be  used,  but  in  my  opinion  whenever  it 
becomes  necessary  in  concentrating  to  pulverize  very  completely 
material  with  a  hard,  tough  gangue,  that  duty  should  be  assigned 
to  a  Chilean  mill.  Wet  crushing  between  close  size  limits  is 
premised  in  every  case. 

A  fault  of  the  Huntington  mill  is  the  uneven  wearing  of  the 
roller  rings.  Instead  of  wearing  evenly  to  successively  smaller 
concentric  circles,  they  frequently  assume  polygonal  shapes  and 
then  pound  around  the  inside  of  the  die  ring  instead  of  rolling  in 
continuous  contact  with  it.  When  this  fault  becomes  aggravated 
the  grinding  falls  to  a  fraction  of  the  normal  capacity,  and  the 
machine  becomes  a  deafening  rattle-box.  The  new  6-ft.  mills 
running  at  52  revolutions  per  minute  in  the  west  half  of  the  new 
mill  at  Anaconda  show  a  very  considerable  increase  in  capacity 
over  the  smaller  ones.  They  run  more  smoothly,  wear  the  roller 
and  die  rings  more  evenly,  and  are  a  considerable  improvement  in 
every  way. 

The  rolls  tested  were  Gates'  heavy  pattern,  with  shells  15  in. 
by  36  in.,  run  at  108  revolutions  per  minute,  giving  a  peripheral 
speed  of  1018  ft.  per  minute.  The  usual  arrangement  of  rolls 
and  trommels  was  used,  in  which  the  feed  first  passes  to  an 
elevator,  then  to  the  trommels,  the  under-size  going  to  jigs  and 


126  METALLURGICAL  MILL  CONSTRUCTION 

the  over-size  to  the  rolls.  After  passing  the  rolls  the  crushed 
material  joins  the  incoming  feed  and  goes  up  in  the  elevator  to 
the  trommels  again. 

The  most  conspicuous  feature  of  the  roll  product  is  the  small 
quantity  of  slimes  present.  When  the  minerals  which  will  make 
a  desirable  concentrate  can  be  set  free  by  crushing  the  containing 
tailings  to  pass  1.5  or  1.25  mm.  there  is  no  machine  so  well  adapted 
to  do  it  as  rolls.  On  such  material  the  recovery  of  concentrates 
after  roll-crushing  exceeds  the  recovery  following  any  other 
machine.  Their  capacity  is  far  in  excess  of  any  other  regrinding 
machine,  crushing  to  the  same  size.  But  the  lower  limiting  size 
is  reached  here,  unfortunately.  The  mechanical  difficulties 
present  in  the  rolls  themselves,  which  lower  their  effectiveness 
when  crushing  to  a  finer  size,  as  well  as  the  impracticability  and 
low  efficiency  of  trommels  using  a  finer  cloth,  has  hitherto  pre- 
vented their  use  for  finer  grinding. 

However,  the  day  is  confidently  looked  for  when  rolls  will 
supersede  the  Huntington  mill,  which  is  now  the  machine  best 
suited  to  the  regrinding  of  material  to  sizes  finer  than  1.25  mm. 
when  the  avoidance  of  slimes  is  a  prime  necessity.  Hydraulic 
classification  may  take  the  place  of  the  trommel  in  the  roll  system 
and  return  the  coarse  size  to  the  machine,  which  with  improve- 
ments in  the  rolls  themselves,  in  the  metal  of  the  shells  and  in 
methods  of  distributing  the  feed  so  as  to  cause  more  even  wear, 
will  undoubtedly  enable  rolls  to  do  finer  work  than  they  are  now 
assigned  to. 


REGRINDING  MACHINERY 

BY  S.  V.  TRENT 

(March  31,  1904) 

I  have  read  with  much  interest  the  statement  of  tests  made  by 
Martin  Schwerin  in  the  Engineering  and  Mining  Journal  of  March 
10.  Having  given  a  good  deal  of  study  and  observation  to  the 
matter  of  crushing  and  pulverizing  machinery,  I  am  naturally 
interested  in  a  subject  of  this  kind,  especially  as  I  happen  to  be 
familiar  with  the  operations  at  Anaconda. 

While  I  believe  Mr.  Schwerin's  conclusions  are  in  the  main 
sound  and  correct,  I  believe  his  generalizations  in  regard  to 
Chilean  mills,  Huntington  mills,  rolls,  etc.,  are  very  far  from 
final,  and  that  he  himself  will  be  willing  to  admit  this,  after  con- 
sideration of  certain  features  that  he  entirely  overlooks  in  the 
article  in  question.  Furthermore,  there  is  one  all-important 
feature  developed  by  the  earlier  tests  at  Anaconda  of  which  he 
makes  absolutely  no  mention.  I  refer  to  the  fact  that  in  the 
comparison  between  the  Monadnock  mills  that  were  used  in  the 
old  plant  of  the  upper  works,  as  compared  with  the  performance 
of  crushing  rolls,  Gates  and  others,  doing  similar  work,  it  was 
found  that  the  final  tailings  from  the  tables  taking  their  feed 
from  the  Monadnock  mills  showed  a  much  lower  residue  of  copper, 
ranging  from  0.5  to  0.6  per  cent.  On  the  other  hand,  the  tailings 
from  tables  taking  their  feed  from  the  crushing  rolls  of  different 
makes  showed  an  average  copper  content  varying  between  0.85 
and  0.95.  This  was  indeed  a  revelation,  and  could  only  be 
accounted  for  on  the  supposition  of  a  more  favorable  form  of 
grinding  by  the  mills,  as  compared  with  the  simple  cracking 
operation  of  the  rolls  that  Mr.  Schwerin  lays  such  stress  upon. 

As  regards  the  Evans-Chilean  mill,  whose  work  was  the  basis 
of  the  test  report  referred  to,  Mr.  Schwerin  overlooks  the  fact 
that  it  was  proportioned  with  extremely  bad  judgment  for  the 
work  to  be  accomplished.  Mills  of  the  Chilean  type,  when  pro- 

127 


128  METALLURGICAL  MILL  CONSTRUCTION 

portioned  intelligently  for  the  required  work,  are  capable  of 
almost  infinite  variation.  If  a  pulverizing  machine  proportioned 
for  handling  the  hardest  of  rock  is  used  upon  soft  or  friable 
quartz,  unsatisfactory  results  must  of  course  be  anticipated,  in 
the  same  way  as  improper  results  will  accrue  where  pulverizing 
machinery  adapted  for  soft  ore  is  used  upon  the  hardest.  What 
I  mean  to  say  is  this  —  that,  with  the  Chilean  form  of  mill  properly 
proportioned,  the  percentage  of  fines  is  very  largely  under  control. 

Of  course,  the  longer  material  remains  in  a  pulverizing  machine, 
the  more  finely  it  will  be  pulverized,  the  supposition  being  that  a 
machine  is  at  all  times  receiving  a  feed  properly  calculated  for  its 
capacity.  Where  a  properly  designed  Chilean  mill  of  large  capac- 
ity is  called  upon  to  do  its  work  on  a  reduced  capacity,  it  is 
simply  a  question  of  reducing  the  speed  of  the  mill  to  get  a  reduced 
capacity  without  producing  excessive  fines,  and  with  a  crushing 
force  properly  proportioned  to  the  hardness  and  size  of  the  feed, 
the  proportion  of  fines  can  be  kept  under  good  control. 

Furthermore,  I  must  take  exception  to  Mr.  Sehwerin's  dictum 
that  "wet  crushing  between  close  size  limits  should  be  premised 
in  every  case."  Using  the  form  of  Chilean  mill  with  which  I  am 
particularly  identified,  it  i$  entirely  feasible,  even  with  very  hard 
rock,  to  take  a  feed  of  up  to  2  or  3  in.,  and  reduce  to  anywhere 
from  20-  to  60-mesh  at  the  one  operation,  without  any  material 
detriment  to  the  machine. 

Again,  referring  to  that  paragraph  concerning  crushing  rolls, 
from  which  I  quote  the  following:  "The  most  conspicuous  feature 
of  the  roll  product  is  the  small  quantity  of  slime  present."  Of 
course,  where  a  machine  does  not  pulverize,  but  simply  crushes, 
as  in  the  case  of  rolls,  as  much  slime  may  not  be  produced  as  from 
a  strictly  pulverizing  operation;  but  if  the  copper  remains  in  the 
final  tails,  what  practical  advantage  is  there  in  the  suppression 
of  fines? 

I  also  wish  to  challenge  this  further  statement:  "Their  [crush- 
ing rolls]  capacity  is  far  in  excess  of  any  other  regrinding  machine 
crushing  to  the  same  size."  Taking  a  Chilean  mill  of  the  size 
and  weight  that  Mr.  Schwerin  refers  to,  it  is  entirely  feasible  to 
arrive  at  a  pulverizing  capacity  of  12  tons  per  hour,  pulverizing 
through  1.25  mm.  screen,  as  against  the  9  tons  per  hour  that 
Mr.  Schwerin  quotes  as  the  capacity  of  the  36  by  15  in.  rolls. 
From  Mr.  Schwerin's  table  of  tests  it  would  appear  that  the 


ORE-CRUSHING  MACHINERY  129 

extreme  range  of  the  Chilean  mill  rises  to  8  tons  per  hour,  but 
that  is  by  no  means  the  limit. 

The  auxiliary  machines  incidental  to  crushing  rolls  on  this 
class  of  work,  comprising  elevators  and  fine  screens,  is  a  matter 
that  Mr.  Schwerin  passes  over  lightly,  but  they  are  serious 
features,  especially  in  a  plant  of  large  capacity. 


REGRINDING  MACHINERY 

BY  GEORGE  E.  COLLINS 

(April  21,  1904) 

I  have  been  greatly  interested  in  the  valuable  notes  con- 
tributed by  Mr.  Schwerin  under  the  above  heading,  and  from 
my  own  experience  can  endorse  most  of  his  conclusions. 

Rolls  are  sometimes  preferable,  because  of  the  minimum 
proportion  of  slimes  produced;  but  their  capacity  is  small  when 
fine  crushing  —  under  20-  or  30-mesh  —  is  necessary.  Moreover, 
unless  the  entire  product  is  made  to  pass  through  a  screen  of 
finer  mesh  than  the  smallest  particles  of  the  feed,  the  same  objec- 
tion which  Mr.  Schwerin  raises  to  Krupp  mills  for  regrinding  for 
subsequent  concentration  applies  to  rolls  in  even  greater  degree 
—  that  much  of  the  material  passes  through  without  any  re- 
crushing  at  all. 

Huntingtons  slime  less  than  Chilean  mills,  and  for  a  friable 
ore  are  preferable;  but  with  a  hard  and  tough  gangue  they  often 
fail  to  pulverize,  making  a  large  proportion  of  rounded  gravelly 
particles. 

The  Chilean  mill  —  of  which  I  have  had  experience  only  with 
the  Monadnock  type,  built  by  Messrs.  Trent  —  is  the  most  widely 
useful  machine  I  know  of  for  moderately  fine  regrinding.  One 
of  its  drawbacks,  to  which  neither  Mr.  Schwerin  nor  Mr.  Trent 
alludes,  is  the  variation  in  product  and  output  as  die  and  rings 
wear  down:  in  the  former  case  owing  to  increasing  hight  of 
discharge,  as  in  a  stamp-mill;  in  the  latter  because  of  lessened 
weight  of  mullers.  This  variation  cannot  be  closely  controlled 
by  changing  the  screen-mesh;  and  is  only  partially  obviated  by 
care  in  keeping  the  scrapers  close  to  the  die. 

The  same  point  which  Mr.  Schwerin  notes  with  Huntington 
mills  —  irregular  wearing  of  rings  and  dies  —  often  applies  in 
less  degree  to  Chilean  mills.  I  agree  with  Mr.  Trent  that  the 
Monadnock  mill  can  successfully  reduce  comparatively  coarse 

130 


ORE-CRUSHING  MACHINERY  131 

feed  to  any  desired  mesh  at  one  operation,  without  proportionately 
reducing  capacity;  so  can  the  Huntington.  I  doubt,  however, 
whether  2-  to  3-in.  sizes  can  be  fed  with  advantage,  as  this  results 
in  undue  strains  on  running  gear  and  foundations. 

I  am  disposed  to  think  that  the  importance  of  gradual  reduc- 
tion —  the  cracking  of  each  grain  once  only  —  is  often  overrated. 
The  carrying  of  this  ideal  into  practice  sometimes  results  in  the 
circulation  round  and  round,  in  trommels  and  elevators,  of  a 
great  bulk  of  middlings,  the  more  friable  (and  usually  the  richest) 
constituents  of  which  are  often  literally  worn  away.  It  will 
frequently  pay  better  to  recrush  a  little  finer,  at  one  stage. 

Similar  experiments  to  those  of  Mr.  Schwerin  in  really  fine 
grinding  —  below  100-mesh  —  of  hard  ores  would  be  valuable. 
In  the  case  of  the  Cornish  tin-ores,  for  instance,  much  of  the 
mineral  is  often  not  liberated  without  very  fine  grinding.  For 
this  work,  in  my  time,  the  Stephens-Toy  pulverizer  was  largely 
used,  a  machine  obviously  modeled  on  the  pans  used  in  pan- 
amalgamating.  This  machine  held  the  field,  notwithstanding  ats 
heavy  costs  in  power  and  repairs.  For  such  extremely  fine 
grinding,  there  was  obviously  reason  for  the  local  use  of  discharge 
by  " flush"  in  place  of  screens.  Possibly  the  Gilpin  county 
burr-slot  screen  would  have  answered. 

In  some  recent  laboratory  experiments  in  the  concentration 
of  a  wolfram  ore,  I  found  that  only  a  very  imperfect  separation 
could  be  effected  without  crushing  to  80-mesh;  and  even  after 
regrinding  to  100-mesh  there  was  a  considerable  proportion  of 
middlings  which  needed  still  finer  grinding.  Nothing  short  of  the 
regrinding  such  as  is  done  by  the  Cornish  " streamers"  on  the  Red 
River  and  elsewhere  would  have  liberated  this  mineral  so  as  to 
permit  of  a  clean  product  being  obtained. 


THE  FERRARIS  BALL-MILL 

BY  W.  R.  INGALLS 

(November  28, 1903) 

The  Ferraris  mill  is  a  new  device  of  the  ball-mill  type,  espe- 
cially adapted  for  wet-crushing,  which  is  now  in  successful  use  at 
the  works  of  the  Societa  di  Monteponi,  at  Monteponi,  Sardinia, 
and  at  the  works  of  the  Societe  Miniere  du  Gard  at  Durfort, 
France.  At  both  places  it  is  employed  for  the  fine  crushing  of 
mixed  sulphide  ores  as  a  preliminary  to  separation  on  shaking 
tables.  Other  installations  besides  those  mentioned  are  shortly 
to  be  made.  As  a  machine  for  fine  crushing  the  mill  is  especially 
interesting  because  of  its  simplicity,  and  therefore  its  compara- 
tively low  cost.  It  is  the  invention  of  Signor  Erminio  Ferraris, 
the  director-general  of  the  Societa  di  Monteponi. 

The  general  construction  of  the  mill  is  shown  in  the  accom- 
panying engravings.  A  steel  drum  is  divided  into  two  compart- 
ments by  a  perforated  annular  partition.  The  larger  compart- 
ment, into  which  the  ore  is  fed,  is  lined  with  hard  steel  plates, 
and  contains  the  usual  balls  for  crushing  the  ore.  The  smaller 
compartment  is  divided  into  a  series  of  pockets  by  means  of  a 
cone,  protruding  into  the  larger  compartment,  and  a  series  of 
radial  partitions  extending  thereform.  The  ore,  having  been 
crushed  to  a  certain  degree  in  the  larger  compartments,  escapes 
through  the  holes  in  the  partition  into  the  smaller  compartment. 
If  it  has  been  crushed  to  the  desired  fineness,  it  is  discharged 
through  the  screens  in  the  end  of  the  drum;  otherwise,  it  is  elevated 
in  the  radial  pockets  of  the  smaller  compartment,  by  the  rota- 
tion of  the  drum,  until  it  slides  back  on  the  surface  of  the  cone 
into  the  larger  compartment,  where  it  undergoes  further  crush- 
ing. 

The  steel  drum  is  supported  on  four  bearing  rollers,  which 
are  driven  by  suitable  mechanism,  turning  the  drum  by  friction 
around  its  longitudinal  axis.  The  tires  are  made  of  cast  steel 

132 


ORE-CRUSHING  MACHINERY 


133 


and  the  rollers  of  chilled  cast  iron.  The  shell  of  the  drum  is 
made  of  f-in.  wrought  iron  or  steel  plate,  and  the  drum  is  divided 
by  an  annular  perforated  partition  into  the  two  compartments 
above  described.  In  the  mills  in  use  at  Monteponi  the  larger 
compartment  is  about  56  in.  in  diameter  and  33  in.  in  length. 
About  800  Ib.  of  balls  are  used  therein,  the  balls  varying  in  size 
from  6  in.  diameter  down  to  3  in.  It  is  necessary  to  have  balls 
of  different  sizes  in  order  to  effect  the  crushing.  The  balls  must 
be  made  of  forged  steel;  if  made  of  cast  steel  without  forging, 
they  will  not  remain  spherical  as  they  wear  down  in  use.  The 


TRANSVERSE 
SECTION 


FIG.  17.  —  Ferraris  Ball-Mill. 

crushing  compartment  is  lined  with  bars  of  cast  steel,  1.5  in. 
thick,  with  projecting  ribs.  The  form  of  the  ribs  need  not  be 
precisely  as  shown  in  the  drawings;  under  certain  circumstances, 
bars  of  trapezoidal  form  might  be  preferable.  The  lining  need 
not  be  adjusted  precisely,  because  the  crushed  ore  will  fill  the 
spaces.  At  Monteponi  the  rough  bars  are  put  in  just  as  they 
come  out  of  the  mold. 

The  smaller  compartment  of  the  drum  is  about  8  in.  in  length. 
The  peripheral  holes  in  the  dividing  partition  are  0.6  in.  in  diam- 
eter on  the  side  of  the  larger  compartment,  and  1  in.  in  diameter 


134 


METALLURGICAL  MILL  CONSTRUCTION 


on  the  side  of  the  smaller.  The  size  of  these  holes  should  vary 
according  to  the  kind  of  ore  to  be  crushed.  If  the  ore  has  an 
especial  tendency  to  slime,  it  will  be  advisable  to  make  the  holes 
larger  than  otherwise  in  order  to  let  the  material  more  quickly 
out  of  the  crushing  compartment,  giving  the  fine  stuff  an  oppor- 
tunity to  pass  out  through  the  delivery  screens,  the  larger  pieces 
being  returned  to  the  crushing  compartment  for  further  re- 
duction. 

The  cylinder  is  rotated  at  20  r.  p.  m.     They  have  been  op- 
erated at   16  and  at  30  r.  p.  m.,  but  their  efficiency  has  been 


FIG.  18.  —  Ferraris  Ball-Mill. 

proved  to  be  greatest  at  20  revolutions.  The  mill  has  crushed 
4000  kg.  of  quartzose  ore  to  pass  a  3-mm.  screen  in  three  hours, 
the  feed  being  in  lumps.  This  is  8818  Ib.  or  2939  Ib.  per  hour, 
or,  say,  1.5  short  tons,  equivalent  approximately  to  30  tons  per 
day  of  20  hours.  In  the  case  of  a  sandstone  finely  impregnated 
with  blende,  fed  both  in  lumps  and  smalls,  the  capacity  was 
1250  kg.  per  hour,  crushing  to  1  mm.  size. 

The  advantages  of  ball-mills  as  a  type  of  crushing-machine 
are  that  they  combine  in  one  apparatus  the  means  for  pulverizing 


ORE-CRUSHING  MACHINERY  135 

and  screening  the  ore  and  the  return  of  the  oversize;  at  the  same 
time  it  is  a  machine  which  occupies  relatively  little  room,  either 
superficially  or  in  hight,  receives  ore  in  large  pieces  and  reduces 
it  to  fine  size  in  one  operation,  and  consumes  comparatively  little 
power  per  ton  of  ore.  Its  chief  disadvantage  is  the  large  con- 
sumption of  steel  through  wear  of  the  balls  and  the  lining,  which 
is  not,  however,  so  large  as  to  offset  the  advantages.  In  the 
Ferraris  mills  at  Monteponi  this  wear  amounts  to  100  kg.,  or 
220  Ib.  in  a  month,  working  10  hours  daily.  In  crushing  1.5  tons 
of  ore  per  hour  to  3  mm.  size,  this  would  figure  out  to  about 
0.6  Ib.  of  steel  per  ton  of  ore. 

Contrary  to  the  belief  of  many  who  are  not  practically  familiar 
with  the  ball-mills  as  a  type,  they  make  a  granular  product,  not 
a  slimy  one.  The  Ferraris  ball-mill  is  designed  especially  for 
wet-crushing,  and  is  used  very  advantageously  in  connection  with 
bumping  or  shaking  tables  for  the  concentration  of  ores  that 
require  grinding  to  1-mm.  size  (about  12-rnesh)  or  finer.  It  is 
used  in  this  way  at  Monteponi  and  at  Durfort,  France.  Screens 
being  entirely  dispensed  with  and  belt  elevators  and  power- 
transmitting  mechanism  being  reduced  to  the  minimum,  the  cost 
of  plant  is  much  reduced,  there  being  also  a  saving  in  the  building, 
which  can  be  made  comparatively  small  in  floor  area  and  of  little 
hight.  Thus  a  concentrating  plant  of,  say,  50  tons  capacity  per 
day  can  be  obtained  by  installation  of  one  9-  by  15-in.  crusher, 
one  short  belt  elevator  to  deliver  into  the  ball-mills,  two  ball- 
mills,  one  hydraulic  classifier  and  four  Wilfley,  or  similar  tables, 
and  a  40-  to  50-horse-power  engine.  The  expense  for  operation 
is  also  reduced  to  the  minimum,  since  the  ball-mills  require  very 
little  attention. 

As  compared  with  stamps,  the  ball-mill  is  the  more  economical. 
This  is  shown  by  the  results  of  certain  tests  reported  in  the 
Engineering  and  Mining  Journal,  Nov.  9,  1901,  page  602.  A  five- 
stamp  battery  with  a  stamp  weight  of  525  kg.  (about  1.165  Ib.), 
falling  160  mm.  (about  6.5  in.),  with  92  drops  per  minute,  crushed 
approximately  780  kg.  (about  1720  Ib.)  of  hard  quartz  per  hour 
through  a  40-mesh  screen,  requiring  12.5  horse-power.  A  No.  3 
Krupp  ball-mill  crushing  wet,  with  450  kg.  of  special  steel  balls, 
passed  1200  kg.  (about  2650  Ib.)  of  the  same  quartz  through  the 
same  screen  per  hour,  using  only  9  horse-power.  Of  the  material 
crushed  by  the  stamps  to  pass  a  40-mesh  sieve,  only  6.5  per  cent. 


136  METALLURGICAL  MILL  CONSTRUCTION 

was  retained  on  a  60-mesh  sieve,  while  in  the  case  of  the  ball-mill 
product  32.6  per  cent,  would  not  go  through  a  60-mesh  sieve. 
Of  the  product  of  the  stamps,  56.5  per  cent,  was  fine  enough  to 
pass  a  150-mesh  sieve,  as  compared  with  33.8  per  cent,  of  the 
ball-mill  product. 


THE  OPERATION  OF  A  TUBE-MILL  * 

BY  HERMANN  FISCHER 

(November  17,  1904) 

The  operation  of  grinding  in  a  tube-mill  is  carried  out  in  a 
closed  receptacle;  one  can  only  see  the  incoming  and  outgoing 
material  and  hear  the  noise  in  the  interior  of  the  revolving  drum. 
As  for  the  rest,  one  must  fall  back  upon  a  comparison  with  known 
operations  of  an  analogous  character.  For  this  reason,  the 
opinion  has  been  generally  held  that  the  balls  roll  on  the  slope 
of  the  drum,  inside  the  whirling  mass,  crushing  the  ore  between 
them,  until  it  passes  from  the  feed  to  the  discharge  at  the  lower 
end  of  the  drum. 

By  means  of  special  arrangements,  the  firm  Fried.  Krupp 
A.-G.  Grusonwerk,  of  Magdeburg-Buckau,  have  now  rendered  it 
possible  to  observe  the  operations  in  the  interior  of  the  drum. 
These  observations  prove  that  the  explanation  hitherto  accepted 
is  fundamentally  wrong,  that  the  tube-mill  does  not  appreciably 
grind  the  ore,  either  on  the  slope  or  in  the  interior  of  the  whirling 
mass,  but  crushes  it  by  an  inclined  beating  action,  and  that  the 
higher  position  of  the  feed,  as  compared  with  the  discharge,  is 
of  no  importance  for  conveying  the  material. 

For  the  purpose  of  experiment,  a  glass  drum  was  first  used; 
then  a  larger  one  was  constructed,  in  which  the  inspection  of 
the  interior  of  the  drum  was  rendered  possible  by  an  exchangeable 
grating,  and,  finally,  a  drum  of  1  m.  (39f  in.)  interior  diameter, 
of  similar  construction,  was  employed.  This  was  first  operated 
without  material,  and  then  with  material  of  different  kinds, 
which  would  not  give  off  dust,  at  varying  speeds  of  rotation. 

The  discharge  end  of  the  drum  was  closed  only  by  a  wire 
grating,  Figs.  19  and  20,  so  that  the  interior  was  clearly  visible. 
The  drum  contained  only  flint  balls,  about  60  mm.  (2f  in.)  in 

1  Abstract  of  a  paper  in  the  Zeitschrift  des  Vereines  Deutscher  Ingenieure, 
March,  1904. 

137 


138 


METALLURGICAL  MILL  CONSTRUCTION 


FIG.  19.  —  Beginning  of  Rotation. 
1  Meter  Diameter. 


diameter.  The  hight  of  arch  of  this  charge  was  about  450  mm. 
(17j  in.)  when  the  drum  was  in  a  state  of  rest.  The  drum  was 

then  turned  slowly  by  hand, 
until  a  few  balls  began  to 
move  on  the  surface.  Fig.  19 
represents  this  stage.  Then 
the  speed  was  raised  to  21  and 
23 J  revolutions  per  minute; 
the  balls  rolled  rather  slowly 
down  the  slope;  the  hight  of 
the  mass  increased  a  little. 
As  the  speed  increased  to  28, 
30,  and  32  revolutions  per 
minute,  the  motion  on  the 
free  side  became  more  lively, 
and  the  mass  became  visibly 
loose;  the  hight  increased  to 
about  600  mm.  (23f  in.).  Fig. 
20  is  an  instantaneous  view  of 
the  operation  when  the  drum  was  revolving  at  32  revolutions  per 
minute.  The  balls,  which  are 
in  contact  with  the  drum  be- 
low and  on  the  ascending  side, 
are  carried  along  without 
changing  their  position  rela- 
tively to  the  wall  of  the  drum, 
until  they  separate  therefrom 
at  a  certain  hight  and  de- 
scribe a  distinct  curve  of 
projection.  The  balls  further 
inward  likewise  do  not  change 
their  position  with  regard  to 
the  drum  when  ascending, 
but  a  curve  of  projection  is 
hardly  perceptible  on  the  de- 
scending side.  On  comparing 
Fig.  20  with  Fig.  19,  it  will 

be  seen  that  the  contents  have  become  looser.  As  the  speed 
accelerates  to  35  revolutions  per  minute,  this  tendency  is  more 
marked,  so  that  the  hight  increases  to  650  mm.  (25f  in.).  The 


FIG.  20.  —  Mill  1  Meter  Diameter. 
32  Revolutions. 


ORE-CRUSHING  MACHINERY 


139 


FIG.  21.  — Mill  300  mm.  Diameter. 
59  Revolutions. 


curve  of  projection  of  the  balls,  which  were  raised  when  in  con- 
tact with  the  drum,  is  clearly  visible,  as  is  also  the  fact  that  the 
balls  further  inward  are  sepa- 
rated in  layers.  On  the  as- 
cending side,  about  200  mm. 
(7J  in.)  from  the  wall  of  the 
drum,  a  few  balls  roll  in  a 
hollow  space  of  oval  cross- 
section  without  intermingling 
with  those  moving  further 
onward.  The  hollow  spaces 
between  the  several  layers 
on  the  descending  side  are 
visible  throughout,  while  on 
the  ascending  side  the  layers 
are  close  to  each  other.  Figs. 
21  and  22  are  instantaneous 
views,  obtained  with  a  drum, 
300  mm.  (lljf  in.)  in  di- 
ameter and  revolving  at  59  and  66  revolutions  per  minute.  A 

comparison  shows  clearly  how 
the  looseness  of  the  contents 
increases  with  the  speed.  If 
the  speed  of  rotation  is 
further  increased,  the  balls 
form  a  solid  ring,  revolving 
with  the  drum;  a  shifting  of 
the  balls  is  not  perceivable. 
Fig.  23  is  an  instantaneous 
view,  when  the  drum  is  re- 
volving at  a  speed  of  55  revo- 
lutions per  minute. 

A  large  quantity  of  mate- 
rial, producing  no  dust,  was 
now  introduced.  This  mate- 
rial, moving  in  the  same 
manner  as  the  balls,  as  was 

anticipated,  entered  the  hollow  spaces  between  the  balls,  and 
ascended  and  descended  with  them.  A  difference  was  only  notice- 
able in  so  far  as  the  precipitated  layers  were  less  sharply  marked, 


FIG.  22.  —  Mill  300  mm.  Diameter. 
66  Revolutions. 


140 


METALLURGICAL  MILL  CONSTRUCTION 


and  the  particles  of  material  were  spurted  laterally,  especially  at 
that  spot  which  was  hit  by  the  mixture  rushing  down  like  a  water- 
jet.  Hardly  any  material  was  noticed  in  the  contracted  oval  hol- 
low space. 

I  have  already  stated  that  a  sliding  or  rolling  motion  between 
the  balls,  or  between  the  balls  and  material,  does  not  take  place 
except  at  the  striking  point  and  in  the  oval-shaped  hollow  space. 
Since  the  latter  is  almost  free  from  material,  a  crushing  action  — 

at  least,  one  of  any  impor- 
tance —  can  take  place  only 
at  the  striking  point,  where 
the  falling  balls  are  violently 
forced  upon  the  material  be- 
tween them  and  the  balls 
which  have  been  previously 
operating.  The  former  play 
the  part  of  the  shoes  in  a 
stamp-battery,  and  the  latter 
act  as  a  substitute  for  the 
dies.  The  crushing  is  effected 
by  stamping  or  beating.  The 
action,  however,  differs  from 
that  in  stamp-batteries,  in  so 
far  as  the  horizontal  motion 
of  the  falling  balls  is  oppo- 
site to  that  of  the  balls  revolving  with  the  drum. 

Owing  to  the  force  of  the  strokes,  the  balls  near  the  striking 
point  will  undergo  a  certain  displacement,  which,  however,  can 
hardly  produce  a  crushing  action  of  any  importance.  The 
crushing  action  thus  depends  on  the  hight  of  fall  of  the  balls  — 
that  is,  on  the  hight  of  the  vertex  of  the  path  of  projection  over 
that  point  where  the  balls  strike  —  on  the  speed  of  the  drum, 
and  on  the  weight  and  the  number  of  balls.  The  speed  of  the 
drum  must  be  so  chosen  that  the  paths  of  projection  can  be  well 
developed.  Weight  of  balls  and  hight  of  their  fall  supplement 
each  other,  in  so  far  as  they  are  factors  of  a  product.  Harder 
material  requires  heavier  balls,  or  a  greater  hight  of  fall  than 
softer  material,  and  steel  balls  can  have  the  same  efficiency  in 
smaller  drums  as  flint  balls  in  larger  drums.  The  larger  the 
quantity  of  balls  acting  on  a  certain  quantity  of  material,  the 


FIG.  23.  —  Mill  1  Meter  Diameter. 
66  Revolutions. 


ORE-CRUSHING  MACHINERY  141 

better  the  crushing.  If  more  material  of  the  same  kind  is  to  be 
crushed  to  the  same  degree  of  fineness  within  a  certain  period, 
the  quantity  of  balls  —  and,  consequently,  the  length  of  the 
drum  —  must  be  greater.  The  respective  numerical  values  can 
be  obtained  only  on  the  basis  of  extensive  experiments. 

In  the  further  course  of  the  experiments,  the  discharge  end 
of  the  drum,  Fig.  28,  was  closed  by  means  of  sheet  metal,  having 
in  its  center  a  trellised  opening  of  200  mm.  (7J  in.)  diameter. 
To  the  feed-end  was  fitted  a  hollow  cone,  c,  of  sheet  metal.  The 
opening  of  this  cone  on  the  drum  side  —  500  mm.  (19  \^  in.) 
diameter  —  was  trellised  and  partly  covered  by  a  fixed  plate,  e, 
secured  to  the  machine  frame,  as  represented  in  Fig.  27.  The 
material  was  now  introduced  through  a  manhole,  and  the  drum 
was  set  in  operation  at  the  rate  of  32  r.  p.  m.  A  further  quantity 
of  material  was  thrown  into  c  by  hand-shovels.  It  was  readily 
taken  through  the  free  opening  of  the  grating,  so  that  each  shovel- 
ful rapidly  vanished.  On  the  outlet  side,  the  material  was 
discharged  through  the  meshes  of  the  grating,  conformably  to 
the  curve  of  projection.  The  discharge  of  the  material  thus  took 
place  at  a  considerably  higher  level  than  the  feed-opening. 

Consequently,  the  progressive  motion  of  the  material  from 
the  feed-end  to  the  discharge  —  which  is  required  by  the  tube- 
mills  (ball-mills  without  sieves  at  the  curved  wall  of  the  drum) 
—  does  not  depend  on  a  difference  of  hight  between  inlet  and 
outlet.  It  is  only  necessary  that  the  inlet  opening  be  situated 
where  the  contents  of  the  drum  are  loose  enough  to  receive  the 
material,  or  where  the  drum  is  empty,  and  that  the  moving 
contents  of  the  drum  pass  by  the  outlet.  The  drum  acts  like  an 
elevator;  it  lifts  the  balls  and  material  innumerable  times  to  a 
considerable  hight.  In  view  of  the  sum  of  these  risings,  not 
even  the  greatest  possible  difference  in  hight  between  inlet  and 
outlet  end  would  be  of  any  influence. 

By  what  means  is  the  material  compelled  to  pass  through 
the  drum?  That  material  upon  which  a  falling  ball  drops  will 
spurt  on  all  sides  and  be  taken  up  into  the  neighboring  hollow 
spaces.  If  much  material  is  situated  on  the  point  of  stroke, 
much  material  will  be  distributed  therefrom;  otherwise,  little. 
Consequently,  those  parts  of  the  contents  which  are  richer  in 
material  deliver  more  than  is  returned  by  the  parts  poorer  in 
material,  whereby  the  proportions  of  the  mixture  are  equalized. 


142 


METALLURGICAL  MILL  CONSTRUCTION 


UNIVERSITY 


ORE-CRUSHING  MACHINERY 


143 


Owing  to  the  great  activity  with  which  the  contents  of  the  drum 
rise  and  fall,  it  was  observed  that  some  balls  passed  over  their 
path  twice  during  one  revolution;  this  equalization  takes  place 
very  rapidly.  At  the  discharge  end,  the  material  which  spurts 
aside  passes  through  the  meshes  of  the  lat- 
ticed opening,  while  the  balls  are  retained. 
Thus,  at  this  side,  the  mixture  will  be  poorer 
in  grinding  material,  so  that  the  said  equali- 
zation is  directed  hither. 

Fig.  24  is  a  longitudinal  section,  and  Fig. 
25  a  plan  of  a  tube  or  grit  mill;  Fig.  26  a 
cross-section  of  the  drum;  Fig.  27  a  view  of 
the  feed-end,  and  Fig.  28  a  view  of  the  dis- 
charge end  of  the  mill.     The  drum  has  an 
interior  diameter  of  1200  mm.  (3  ft.  11J  in.), 
an  interior  length  of  5000  mm.  (16  ft.  5  in.), 
and  revolves  at  the  rate  of  29  r.  p.  m.     The 
drum  consists  of  sheet  iron,  12  mm.  (15-32  in.)  thick,  has  cast- 
steel  ends,  and  is  lined  with  hard  cast-iron  plates.     The  grind- 
ing balls  are  introduced  through  a  manhole,  while  the  material  to 
be  crushed  is  fed  and  discharged  through  the  hollow  trunnions 


FIG.  26. 


FIG.  28. 


FIG.  27. 


cast  together  with  the  end  walls.  The  material  passes  first  of  all 
into  the  hopper,  a,  in  which  a  studded  shaft  rotates;  a  longitudi- 
nally grooved  drum,  6,  regulates  the  supply.  This  drum  is  rotated 
by  toothed  wheel  gearing  and  a  pair  of  five-step  pulleys  at  dif- 


144  METALLURGICAL  MILL  CONSTRUCTION 

ferent  speeds,  and  contains  a  few  balls,  which  serve  to  shake  the 
drum,  and  thereby  ensure  the  emptying  of  its  grooves.  The  ma- 
terial supplied  is  moved  by  a  screw-conveyor  into  the  hollow 
trunnion  on  the  left  side,  Fig.  24,  and  then  passes  into  the  drum, 
through  the  latter  and  through  the  grating,  c,  into  the  outlet  trun- 
nion on  the  right  side.  The  inlet  trunnion,  on  the  left  side,  has 
the  blades  which  prevent  the  balls  from  dropping  out.  The  grat- 
ing, c,  is  provided  with  arcuate  slots  of  about  25  mm.  (1  in.)  in 
diameter.  The  material  passes  therefrom  into  a  hopper,  d, 
attached  to  the  trunnion.  A  perforated  screen  is  connected  to 
the  hopper.  The  slots  of  the  screen  are  8  mm.  (T5g  in.)  wide  and 
30  mm.  (1  f\  in.)  long;  they  permit  the  crushed  material  to  drop 
through,  while  very  hard  particles  which  are  not  crushed  and  splin- 
ters of  flint  are  retained  and  subsequently  drop  out  on  the  right 
side,  Fig.  24.  The  sieve  is  enclosed  by  a  casing,  out  of  which  the 
air  is  drawn  by  means  of  the  pipe,  e,  so  that  air  enters  all  perme- 
able parts,  thereby  preventing  the  exit  of  dust.  A  great  advan- 
tage of  the  mills,  in  which  the  material  is  fed  and  discharged 
through  the  hollow  trunnions  of  the  drum,  consists  in  the  facility 
of  rendering  the  same  free  from  dust.  If,  however,  the  discharge 
is  effected  through  slots  in  the  drum  casing  near  to  the  rear  end, 
a  comparatively  tight  closure  is  not  possible,  and  the  non-exit  of 
dust  cannot  be  guaranteed  by  the  suction  of  air. 

These  mills  are  made  with  a  width  of  0.95  to  1.5  m.  (3  ft. 
If  in.  to  4  ft.  11  in.),  and  a  length  of  4  to  8  m.  (13  to  26  ft.). 
The  efficiency  depends  to  a  large  extent  on  the  kind  of  the  material 
treated  and  the  degree  of  fineness  desired,  and,  of  course,  also 
on  the  initial  size  of  grain,  which  is  obtained  by  preliminary 
crushing. 


THE  THEORY  OF  THE  TUBE-MILL l 

BY  H.  A.  WHITE 

(September  23,  1905) 

When  a  tube-mill  is  revolved  at  a  suitable  speed,  some  of  the 
balls  at  a  given  moment  will  be  in  the  air,  falling  in  a  certain 
path,  and  some  will  be  resting  on  the  linings  or  on  the  balls  next 
to  the  linings.  In  order  to  study  the  motion  of  the  balls,  an 
apparatus  was  constructed  representing  a  section  of  a  tube-mill. 
From  a  thin  block  of  wood,  an  8i~in.  circle  was  cut,  and  was 
covered  front  and  back  with  J-in.  plate  glass,  the  joints  being 
sealed  with  rubber.  This  was  placed  in  a  rotatable  holder,  and 
so  connected  with  a  motor  that  any  speed  might  be  obtained 
between  6  and  400  revolutions  per  minute. 

The  pulverizing  action  of  the  tube-mill  is  due  almost  entirely 
to  actual  impact  of  the  falling  balls  in  dry  crushing,  but  where 
the  tube  is  half  full  of  water  conditions  are  modified.  A  ball 
falling  into  two  or  three  feet  of  water  will  not  strike  the  bottom 
with  enough  force  to  do  much  crushing,  and  in  this  case  it  is 
probable  that  the  grinding  action  between  the  balls  does  a  great 
proportion  of  the  work;  the  speed  of  revolution  requires  adjusting 
to  avoid  an  unnecessary  amount  of  practically  wasted  fall,  and 
indeed  would  be  best  regulated  so  that  the  angle  of  repose  of  the 
crushing  material  is  alone  considered. 

With  these  ideas  in  mind,  a  series  of  experiments  wag  made 
with  the  apparatus  described  above,  using  J-in.  glass  beads  to 
represent  the  steel  balls.  The  theoretical  motion  of  the  balls 
was  calculated  trigonometrically,  and  the  calculations  verified 
by  experiment,  seeking  to  arrive  at  the  true  theoretical  motion 
of  the  balls.  Fig.  29  shows  the  paths  of  motion  of  the  balls  when 
the  mill  is  run  at  varying  speeds,  permitting  them  to  fall  through 
the  air.  In  this  drawing  the  large  circle  does  not  represent  the 

1  Abstract  of  a  paper  read  before  the  Chem.,  Met.,  and  Min.  Soc.  of  So. 
Africa,  May  20,  1905. 

145 


146 


METALLURGICAL  MILL  CONSTRUCTION 


diameter  of  a  tube-mill,  but  the  diameter  of  the  central  or  pitch 
line  of  an  outer  layer  of  balls  in  a  mill.  For  instance,  if  a  tube- 
mill  were  20  in.  diameter  inside  the  lining  and  1-in.  balls  were 
used,  the  appropriate  circle  on  the  diagram  would  be  29  in. 
diameter. 

Referring  to  Fig.  29,  a  ball  that  does  not  receive  enough  motion 
to  carry  it  up  and  send  it  off  at  a  tangent  would  have  a  path 
designated  as  zero.  On  receiving  sufficient  momentum  to  carry 
it  to  All,  it  would  describe  a  parabola  of  30  deg. ;  to  ^47/7  =  35 
deg.  16  min.,  or  across  the  perpendicular  center  at  its  lowest 
point;  AV  =  45  deg.,  or  through  the  center  of  the  circle;  A VII 
=  60  deg.;  and  so  on  up  to  90  deg.,  which  represents  the  con- 
dition when  the  balls  would  cling  to  the  lining  continuously,  cen- 
trifugal force  having  more  influence  than  gravity. 


FIG.  29.  —  Paths  of  Motion  in 
Tube-Mill. 


FIG.  30.  —  Movement  of  Balls 
in  Tube-Mill. 


In  practice  there  are  several  layers  of  balls  to  consider;  it  is 
calculated  that  each  particular  ball  tends  to  keep  to  its  own 
layer,  and  that  the  theoretical  movement  of  the  unimpeded  balls 
is  about  as  shown  in  Fig.  30.  The  experiments  showed  that  this 
tendency  of  each  ball  to  keep  to  its  layer  was  approximately  true 
where  the  mill  was  not  crowded  with  balls,  yet  had  sufficient  to 
provide  the  weight  necessary  to  give  enough  friction  between 
balls  and  rim  to  develop  the  theoretical  angle  of  fall.  The  pro- 
portion existing  between  the  number  of  balls  on  the  rim  and 
those  in  the  air,  at  any  given  moment,  may  be  determined  from 
the  time  required  for  each  part  of  the  cycle.  The  balls  in  the 


ORE-CRUSHING  MACHINERY  147 

inner  layers  have  a  much  shorter  cyclic  time  than  those  in  the 
outer,  or,  in  other  words,  having  a  smaller  circle  to  traverse,  at 
the  same  speed  they  come  around  more  quickly. 

It  is  evidently  advisable  to  keep  the  number  of  layers  small, 
so  that  the  effective  fall  may  not  vary  too  far  from  the  maximum, 
but  the  limit  to  this  is  set  by  the  necessity  of  having  enough 
weight  and  by  consideration  of  using  the  full  capacity  of  the 
tube-mill  as  far  as  practicable.  If  the  mill  be  half  filled,  the 
width  of  layers  on  the  rim  cannot  exceed  0.293  of  the  radius  and 
will  depend  on  the  angle  of  departure  of  the  outer  layer.  .  An 
inspection  of  Fig.  30  shows  that  interference  with  falling  balls 
would  be  caused  by  too  many  layers,  and  this  condition  should 
be  determined  in  each  case  by  a  diagram. 

In  the  table  of  diameters  and  revolutions,  on  next  page,  it 
must  be  remembered  that  the  diameters  in  the  first  two  columns 
are  figured  from  the  centers  of  the  balls'  paths  in  their  layers, 
and  not  from  the  diameter  of  the  tube-mill.  In  the  third  column 
are  given  the  theoretical  conditions  when  the  mill  is  half  full  of 
water,  and  the  revolutions  per  minute  required  to  keep  the  balls 
continuously  against  the  lining.  In  the  fourth  column  are  the 
revolutions  per  minute  as  calculated  for  dry  grinding;  and  the 
rotative  speeds  required  to  give  the  curves  from  AH  I  to  AV 
(Fig.  29)  are  shown  in  the  remaining  columns.  The  diameter  of 
the  balls  is  taken  at  1-20  of  the  circle  shown  in  Fig.  29,  and  it 
must  be  borne  in  mind  that  the  relative  size  of  the  balls  affects 
the  result.  The  speeds  found  and  given  in  this  table  closely 
approximate  those  given  by  Hermann  Fischer.1 

I  found  that  the  theoretical  number  of  revolutions,  even  after 
due  allowance  was  made,  required  to  be  exceeded  in  every  case 
to  bring  about  the  desired  result.  For  example,  an  8J-in.  wooden 
circle  half  filled  with  coarse  sand  required  94  revolutions  in  place 
of  90.9  to  make  the  first  layer  continuous.  Some  explanation  of 
this  will  be  noticed  in  the  fact  that  a  single  steel  or  glass  ball  up 
to  IJ-in.  diameter  merely  revolves  on  its  own  axis  when  placed 
in  my  cylindrical  section  driven  at  the  speed  of  400  revolutions 
per  minute.  Even  12  steel  balls  on  glass  driven  at  400  will  not 
rise  up  the  side  when  the  balls  are  as  much  as  J  in.  in  diameter 
and  the  glass  4J  in.  They  simply  revolve  axially  and  jump  a 
little.  It  is  clear  that  a  sufficient  quantity  of  balls  must  be 
1  Zeitschrift  des  Vereines  deutscher  Ingenieuref  March  26,  1904. 


148 


METALLURGICAL.  MILL  CONSTRUCTION 


D 

INCHES 

D 

METKRS 

N 
HALF  FULL; 

ALL 
CONTINUOUS 

N 
0=90° 

N 
0=45° 

N 
0=41°0'43* 

N 
0=40° 

N 
0=35°  15'  51* 

1 

0-025 

297-8 

265-0 

222-9 

2147 

212-5 

201-4 

2 

0-051 

210-6 

187-4 

157-6 

151-8 

150-3 

142-4 

3 

0-076 

171-9 

153-0 

128-7 

124-0 

122-7 

116-3 

o-ioo 

133-6 

4 

0-102 

148-9 

132-5 

111-4 

107-3 

106-2 

100-7 

5 

0-127 

133-2 

118-5 

99-68 

96-02 

95-03 

90-07 

6 

0-152 

121-6 

108-2 

90-99 

87-65 

86-75 

82-22 

7 

0-178 

112-6 

100-2 

84-24 

81-15 

80-32 

76-12 

0-200 

94-46 

8 

0-203 

105-3 

93-71 

78-80 

75-91 

75-13 

71-20 

81 

0-216 

102-1 

90-91 

76-44 

73-64 

72-89 

69-08 

9 

0-229 

99-27 

88-35 

74-29 

71-57 

70-83 

67-13 

0-300 

77-12 

12 

0-305 

85-96 

76-51 

64-34 

61-98 

61-34 

58-14 

15 

0-381 

76-89 

68-44 

57-55 

55-44 

54-87 

52-00 

0-400 

66-79 

18 

0-457 

70-19 

62-47 

52-53 

50-61 

50-09 

47-47 

0-500 

59-74 

21 

0-533 

64-99 

57-84 

48-64 

46-85 

46-37 

43-95 

0-600 

54-53 

24 

0-609 

60-80 

54-10 

45-50 

43-83 

43-38 

41-11 

27 

0-686 

57-31 

51-00 

42-89 

41-32 

40-90 

38-76 

0-700 

50-49 

30 

0-772 

54-37 

48-39 

40-69 

39-20 

38-80 

36-77 

0-800 

47-23 

33 

0-838 

51-84 

46-14 

38-80 

37-38 

36-99 

35-06 

0-900 

44-53 

36 

0*914 

49-63 

44-17 

37'15 

35-79 

35-42 

33-57 

39 

0-991 

47-69 

42-44 

35-69 

34-38 

34-03 

32-25 

1-000 

47-46 

42-24 

35-52 

34-22 

33-87 

32-10 

42 

1-077 

45:95 

40-90 

34-39 

33-13 

32-79 

31-07 

•100 

40-28 

45 

•143 

44-39 

39-51 

33-23 

32-00 

31-68 

30-02 

•200 

38-56 

L48 

•219 

42-98 

38-25 

32-17 

30-99 

30-67 

29-07 

51 

•295 

41-70 

37-11 

31-21 

30-06 

29-76 

28-20 

•300 

37-05 

54 

•382 

40-53 

36-07 

30-33 

29-22 

28-92 

27-41 

•400 

35-70 

57 

•448 

39-45 

35-11 

29-52 

28-44 

28-15 

26-68 

•500 

34-49 

60 

•524 

38-45 

34-22 

28-77 

27-72 

27-43 

26-00 

•600 

33-39 

63 

1-600 

37-52 

33-39 

28-08 

27-05 

26-77 

25-37 

66 

1-686 

36-66 

32-63 

27*43 

26-43 

26-16 

24-79 

1-700 

32-40 

69 

1-753 

35-85 

31-91 

26-83 

25-85 

25-58 

24-25 

1-800 

31-49 

72 

1-829 

35-09 

31-23 

26-27 

25-30 

25-04 

23-73 

2-000 

29-87 

84 

2-134 

32-49 

28-92 

24-32 

23-43 

23-19 

21-97 

2-200 

28-48 

96 

2-438 

30-39 

27-05 

22-75 

21-91 

21-69 

20-55 

2-500 

26-71 

108 

2-743 

28-65 

25-50 

21-45 

20-66 

20-45 

19-38 

3-000 

24-39 

ORE-CRUSHING  MACHINERY  149 

present,  or  friction  between  them  and  the  rim  will  be  insufficient, 
and  there  will  be  relative  slip.  Here  also  may  be  observed  one 
of  the  factors  causing  undue  wear  of  the  liners  and  wasted  energy. 

Another  fault  of  insufficient  balls  was  observed  in  the  very 
uneven  falling  caused  by  interchange  of  balls  among  the  several 
layers  when  the  circle  was  less  than  a  quarter  full;  but  these 
effects  were  exaggerated  by  the  smallness  of  the  models  used. 

When  water  was  used  alone,  it  was  observed  that  350  revolu- 
tions were  required  to  make  2.2  in.  of  water  in  an  8J-in.  circle 
continuous,  and  it  fell  again  on  reducing  to  217.  A  greater 
amount  of  water  could  not  be  made  continuous  at  400,  nor  could 
any  amount  of  mercury  alone  be  made  continuous  at  this  speed; 
92  revolutions  would  have  been  sufficient  in  the  absence  of  slip. 
In  using  water  in  conjunction  with  glass  beads,  I  notice  that  very 
little  lifting  of  the  water  can  be  seen  on  the  ascending  side,  and 
it  seems  probable  that  in  practice  the  level  of  water  throughout 
the  tube-mill  would  be  very  nearly  that  of  the  outflow.  In  a 
5-ft.  tube-mill  this  means  that  about  half  the  fall  would  be  through 
water.  A  ball  falling  through  2  ft.  of  water  from  2  ft.  above  it 
would  be  robbed  of  most  of  its  pulverizing  force,  and  this  brings 
us  to  possible  improvements,  suggested  by  theory  and  experi- 
mental data. 

Linings  at  present  seem  to  require  the  presence  of  the  fitter 
or  the  mason  more  than  they  should;  in  fact,  a  duplication  of 
mills  seems  indicated  in  the  absence  of  more  efficient  linings. 
It  seems  barely  possible  that  a  solution  of  this  question  might  be 
had  from  a  continuous  outer  layer  of  balls.  These  would  make 
a  sort  of  automatic  lining;  any  balls  worn  down  would  be  con- 
tinually replaced  and  the  layer  maintained  while  the  mill  is 
running.  A  glance  at  the  table  will  show  that  the  speed  of 
revolution  must  be  kept  constant  and  very  nearly  free  from 
variation. 

Naturally,  a  movable  steel  liner  would  be  used  behind  the 
balls,  but  that  would  only  require  renewal  at  much  longer  intervals 
than  now  necessary.  A  fairly  efficient  fall  would  be  obtained  if 
the  tube  were  filled  about  two-thirds  with  balls.  Of  course, 
while  relying  on  fall  for  crushing  power,  it  is  obvious  that  in  all 
cases  it  cannot  pay  to  waste  energy  in  splashing  water,  and  the 
outlet  must  be  arranged  so  that  depth  of  water  does  not  much 
exceed  depth  of  balls  on  the  bottom  of  the  tube-mill  as  they  are 


15Q  METALLURGICAL  MILL  CONSTRUCTION 

in  motion.  It  does  not  seem  certain  in  wet  crushing  work  that 
the  grinding  effect  between  the  rolling  balls  is  not  of  greater 
importance,  when  the  fineness  of  the  material  and  the  floating 
power  of  the  water  are  borne  in  mind.  If  practical  experience 
determines  this  to  be  the  case,  it  will  only  be  necessary  to  drive 
the  mill  at  such  a  rate  as  will  establish  the  angle  of  fall  of  the 
balls  in  water,  which  may  be  somewhere  about  30  deg.  In  this 
case  the  tube  might  be  somewhat  less  than  half  full,  and  the 
outlet  could  be  arranged  through  a  hollow  trunnion,  as  is  frequently 
clone.  An  advantage  would  be  a  decrease  of  wasted  energy  in 
lifting  balls  worn  down  below  a  useful  size,  which  seems  difficult 
to  obviate  entirely  at  this  time. 

A  practical  method  of  determining  the  best  speed  at  which 
to  run  any  tube-mill  would  be  by  means  of  indicator  diagrams 
or  measurements  of  current  to  determine  when  the  power  absorbed, 
divided  by  the  revolutions  per  minute,  became  a  maximum. 

[In  the  discussion  that  followed  Mr.  White's  paper,  S.  H. 
Pearce  told  of  a  liner  that  was  being  tried  at  Glen  Deep,  which 
was  made  of  rings  of  manganese  steel.  At  first  there  was  a 
noticeable  absence  of  rumbling.  They  noticed  that  the  pebbles 
had  a  tendency  to  wear  flat,  and  that  the  crushing  efficiency 
dropped  considerably.  Later  the  rumbling  was  gradually  re- 
sumed, and  the  crushing  efficiency  increased.  His  conclusion 
was  that  there  was  considerable  slip  on  the  smooth  surface  when 
starting,  and  that  later  the  lining  acquired  a  rough  surface  and 
raised  the  pebbles  a  little  higher,  causing  crushing  instead  of 
reduction  by  attrition. 

W.  R.  Dowling,  of  the  Robinson  Deep  mine,  said  they  had 
two  tube-mills  running,  one  with  manganese  steel  and  the  other 
with  a  silex  lining.  The  latter  mill  took  a  larger  feed  and  gave 
a  finer  ground  product  than  the  manganese;  the  pebbles  also 
retained  their  rounded  shape,  while  with  the  steel  lining  flat 
faces  were  in  evidence,  showing  a  sliding  action.] 


TUBE-MILL  NOTES l 
BY  ALFRED  JAMES 

(March  16,  1905) 

One-stage  wet  tube-mill  work,  that  is,  without  return,  obtains 
not  only  at  El  Oro,  but  in  Korea,  in  Germany,  and  even  at  Kal- 
goorlie  itself,  the  Ivanhoe  having  adopted  this  method  in  pref- 
erence to  the  return  system.  The  Ivanhoe  figures  are  actually 
only  half  those  of  the  other  mines,  which  show  their  cost  per  ton 
milled  instead  of  per  ton  of  sand  absolutely  slimed.  On  the  other 
hand,  the  Ivanhoe  has  recently  thrown  out  its  tube-mill,  evidently 
owing  to  Mr.  Nicholson's  preference  for  pans,  and  it  is  possible, 
therefore,  that  the  cheap  tube-mill  work  accomplished  at  the 
Ivanhoe  may  not  compare  satisfactorily  with  the  more  expensive 
work  accomplished  at  the  Hannan's  Star  or  the  Oroya  Brownhill. 
In  the  latter  case  the  results  are  complicated  by  the  fact  that 
pans  are  used. 

At  first  sight,  the  spitz  separation  of  the  coarse  particles  seems 
undoubtedly  the  proper  method  to  pursue,  but  when  it  comes  to 
passing  268  tons  of  sand  per  diem  through  the  Hannan's  Star 
mill  in  order  to  slime  the  total  sand  output  of  38  tons  only,  it 
looks  as  if  steps  should  be  taken  to  render  unnecessary  such  an 
enormous  amount  of  return,  especially  as  it  is  quite  possible  to 
slime  the  material,  in  one  operation  only,  to  a  fineness  equal  to 
that  of  the  Hannan's  Star  finished  product  —  less  than  5  per  cent, 
retained  on  a  150-mesh  sieve.  In  this  connection  it  is  interesting 
to  note  that  the  costs  given  by  Mr.  Griissner,  as  well  as  by  Mr. 
Broadbridge,  require  to  be  multiplied  by  two  in  order  to  obtain 
the  actual  cost  per  ton  of  sand  slimed  in  the  tube-mill.  Mr. 
Broadbridge's  figures  refer  to  the  total  sand  treated  in  the  agita- 
tion plant,  but  of  this  over  50  per  cent,  has  been  first  separated 
by  a  spitz  and  passes  to  the  plant  without  regrinding,  as  would 
be  obvious  on  examination  of  the  grinding  analysis. 

1  Abstracted  from  contribution  to  discussion,  Institution  of  Mining  and 
Metallurgy,  Jan.  19,  1905. 

151 


152  METALLURGICAL  MILL  CONSTRUCTION 

The  three  division  plates  introduced  into  one  of  the  flint-mills 
at  Kalgoorlie  proved  absolutely  unsuccessful  in  practice.  Manu- 
facturers formerly  made  a  blunder  in  providing  divisions  in  the 
tube,  as  it  is  found  that  the  little  flints  work  their  way  up  the 
tube  through  the  holes  in  the  dividing  plates  and  refuse  to  return; 
they  become  trapped,  and  are  actually  forced  out  at  the  feed 
end  of  the  mill.  Now,  each  mill  is  but  one  long  tube,  and  the 
flints  bed  themselves  perfectly  even.  There  is  no  overlapping  at 
any  particular  spot,  and  no  segregation  of  sizes  whatever. 

As  for  the  great  wear  and  tear  of  lining,  reported  from  the 
Rand,  this  is  due  to  the  deliberate  experimenting  with  coarse 
feed  and  increasing  output;  in  regular  tube-mill  practice  there 
will  be  only  the  usual  consumption  of  lining.  By  "regular  tube- 
mill  practice"  is  meant  the  proportion  of  water  in  feed,  rate  of 
revolution,  weight  and  size  of  flints,  and  size  of  machine,  for 
given  output.  As  no  one  has  given  figures,  with  the  exception 
of  Mr.  Robinson,  who  gave  a  maximum  figure,  it  may  be  added 
that  in  grinding  sand  a  pulp  of  50  per  cent,  thickness  has  been 
found  to  give  good  results,  but  pulp  even  thicker  (60  per  cent.) 
than  this  is  in  successful  use,  so  that  there  are  questions  of  dilu- 
tion, before  the  spitz  and  amalgamation  plates,  which  have  not 
yet  been  fully  considered.  In  the  experimental  work  on  the 
Rand  the  mill  men  naturally  rush  their  feed  through;  that  is 
where  their  experimental  work  necessarily  differs  from  their 
practice.  The  rate  of  revolution  most  satisfactory  in  practice  is 
found  to  be  200  •*•  ^/  D,  where  D  equals  diameter  in  inches. 
Thus  a  4  ft.  1  in.  mill  should  revolve  at  200  •*•  7  =  29,  the  cor- 
rect number  of  revolutions  per  minute.  This  simple  formula  was 
first  suggested  by  Mr.  Davidsen. 

The  correct  charge  of  flints  for  a  mill  is  found  to  be  W  =  44 
X  N,  where  W  equals  the  weight  of  flints  required  and  N  the 
number  of  cubic  feet  contained  in  the  cylinder  of  the  tube-mill; 
but  West  Australian  wet-grinding  practice  takes  nearly  50  per 
cent,  more  flints  than  these  figures.  As  for  the  size  of  flints,  for 
wet-crushing,  large  pebbles  are  found  to  be  best,  say  those  of 
from  3  to  4  in.  diameter.  For  dry-crushing,  smaller  pebbles  give 
a  finer  product. 

In  first  starting  tube-mills  there  is  a  tendency  to  load  up 
with  flints.  Since  experimenting  on  a  large  scale  is  necessarily 
slow  —  as  can  be  seen  by  the  time  which  elapsed  at  the  Hannan's 


ORB-CRUSHING  MACHINERY  153 

Star  before  the  present  high  efficiency  was  obtained  —  it  is 
desirable  not  to  increase  the  load  of  flints  beyond  that  given  by 
makers  without  careful  investigation.  It  is  a  curious  fact,  which 
has  been  noticed  all  over  the  world,  that  it  takes  much  less  horse- 
power to  run  a  tube-mill  crushing  wet  than  crushing  dry. 

One  point,  which  in  practice  has  proved  most  important,  is 
the  need  of  elasticity  in  the  capacity  of  tube-mills.  In  West 
Australia  mills  have  been  put  down  with  the  idea  of  obtaining  a 
unit  of  an  exact  size  to  work  with  uniform  conditions;  but  as 
soon  as  the  stamp  capacity  becomes  increased  the  mills  have  not 
the  elasticity  to  cope  with  the  new  conditions,  and  the  question 
arises,  in  designing  new  installations,  what  size  of  tube-mill 
would  be  most  satisfactory.  It  is  difficult  to  lay  down  a  general 
rule,  but  there  are  two  guiding  principles.  The  first  is  that  a 
tube-mill  working  at  its  full  or  normal  capacity  is  doing  work 
under  the  most  even  conditions,  and,  second,  that  it  is  practically 
impossible  to  increase  the  output  of  a  tube-mill  beyond  its  normal 
capacity.  In  installations  where  an  increased  output  is  being 
worked  it  is  desirable  to  put  in  a  tube-mill  of  greater  capacity 
than  at  first  required,  and  to  revolve  this  more  slowly  than  the 
normal  rate,  or  with  a  less  than  normal  charge  of  flints.  In  this 
way  the  fineness  or  coarseness  of  feed  can  be  regulated  to  a  nicety, 
whereas  the  usual  recipe  of  makers  for  the  regulation  of  the  size 
of  the  finished  product  is  impracticable  with  a  stamp  battery 
which  has  only  a  certain  definite  output,  and  through  which, 
therefore,  one  cannot  rush  a  greater  amount  of  material  in  order 
to  render  the  finished  product  coarser,  and  containing  a  minimum 
proportion  of  slime.  The  better  method  of  accomplishing  this  is 
that  stated  above,  to  diminish  the  flint  charge  or  rate  of  revolution. 


TUBE-MILLS 
BY  H.  W.  HARDINGE 

(June  8,  1905) 

While  the  tube-mill,  or  pebble-mill,  is  not  a  new  device  for 
fine  crushing,  yet  its  application  to  the  milling  of  ore  has  been 
so  successful  as  to  give  it  a  place  among  the  machines  that  con- 
tribute toward  economy  and  efficiency.  Discussions  based  on 
experimental  facts  and  direct  application  are  much  needed. 

The  tube-mill  is  an  exception  to  the  greater  part  of  milling 
machinery  in  that  its  capacity  usually  exceeds  the  estimate;  at 
least,  such  is  my  experience  in  fine  grinding,  wet  or  dry.  I  have 
perused  most  of  the  articles  which  have  come  under  my  notice, 
relative  to  dimensions  of  tube-mills,  the  theory  of  their  operation, 
and  the  results  obtained.  I  realize  that  my  experience  with  a 
tube-mill  (that  I  had  constructed  within  the  last  year)  may 
practically  duplicate  data  already  published;  yet  the  exact  con- 
ditions under  which  I  am  operating  may  be  of  interest  and  use 
to  others.  My  first  experience  with  the  tube-mill,  in  an  experi- 
mental way,  dates  back  eight  or  ten  years,  at  which  time  I  had 
occasion  to  grind  blast-furnace  slag  in  the  dry  way,  and  was  then 
surprised  at  the  results  obtained.  At  the  present  time  I  have 
just  completed  a  1000-ton  wet  test  of  a  very  tough  scale,  the 
composite  average  mesh  of  which  is  given  later. 

The  tube-mills  which  are  now  being  adopted  are  generally 
longer  and  of  less  diameter  than  the  one  I  used  for  wet  grinding, 
which  is  8  ft.  long  by  6  ft.  internal  diameter,  less  the  silex  or 
flint-block  lining,  which  reduces  the  actual  internal  diameter  to 
about  5  ft.  6  in.;  this  mill,  loaded  with  2500  Ib.  of  flint  pebbles 
about  2  in.  diameter,  and  21  revolutions  per  minute,  receives 
6-mesh  ball-mill-crushed  material  and  pulverizes  it  to  the  sizes 
shown  in  the  last  column  given  herewith,  at  a  rate  of  3  tons  per 
hour,  which  is  really  more  than  the  capacity  to  which  the  rest  of 
our  plant  is  adapted.  In  view  of  the  fact  that  2500  Ib.  of  pebble 

154 


ORE-CRUSHING  MACHINERY 


155 


is  not  more  than  one-third  of  the  supposed  or  theoretical  load, 
the  real  capacity  of  this  mill  is  undetermined. 


BALL-MILL 
PRODUCT 

TUBE-MILL 
PRODUCT 

Through    6-mesh 

on  20-mesh  

259% 

0.0% 

"         20-    " 

"40-    "     

13  5 

20 

"         40-    " 

"  60-    " 

90 

85 

"        60-    " 

"  80-    " 

80 

140 

"         80-    " 

400 

755 

96.4 

100.0 

A  few  tons  of  quartzose  ore  gave  a  greater  grinding  capacity. 
Tests  for  consumption  of  pebbles  showed  less  than  1  Ib.  per  ton 
of  ore  treated.  The  wear  upon  the  lining  is  also  slight,  compared 
with  the  result  obtained.  Based  upon  my  present  experience,  I 
have  placed  an  order  for  another  tube-mill  still  further  from  the 
general  practice,  that  is,  6  ft.  long  and  6  ft.  in  diameter. 

Experiments  and  discussion  are  needed  to  determine  the  most 
effective  diameter  and  length  of  mill;  revolution  under  different 
loads;  size  of  pebbles;  whether  pebbles  should  be  of  uniform  or 
different  sizes;  what  relation  size  of  feed  may  have  to  diameter 
of  mill  and  of  pebbles;  what  is  the  most  efficient  feed  and  dis- 
charge; whether  the  action  is  percussive-crushing  or  crushing- 
grinding,  or  a  combination  of  both.  The  capacity  and  small 
load  of  pebbles  in  the  mill  I  now  have  in  use  would  suggest  a 
percussive  effect;  certain  it  is  that  much  less  power  to  operate  is 
required  than  when  a  larger  load  of  pebbles  is  used,  which  would 
lessen  the  useful  duty  of  the  mill,  and  cause  a  needless  attrition 
of  pebbles  and  lining. 


CHILEAN  MILLS 

BY  M.  P.  Boss 

(December  15,  1904) 

The  Chile  mill,  as  its  name  implies,  was  of  Latin  origin,  while 
the  stamp  was  of  Saxon.  In  its  crudest  form  it  was  a  circular 
stone  with  a  hole  through  the  center,  through  which  passed  a 
pole,  one  end  of  which  was  attached  to  a  post,  while  the  other 
end  was  propelled  by  an  animal.  This  machine  was  developed 
in  its  native  environment  into  a  mill  with  two  wheels,  having 
iron  tires  and  driven  by  water  or  steam.  Under  foreign  influence 
it  developed  numerous  modifications,  among  which  are  the  fast- 
motion  edge-running  roller-mills  now  quite  common.  In  its 
original  form,  with  slow  motion,  the  centrifugal  action  or  the 
tendency  to  go  in  a  straight  line,  instead  of  its  circular  course, 
was  not  great,  but  when  it  developed  into  massive  form  or  into 
high  speed,  this  tendency  became  important,  and  different  means 
were  devised  to  neutralize  the  outward  thrust  on  the  axle.  In 
the  massive  slow-motion  mills,  like  those  of  El  Bote  of  Zacatecas, 
or  La  Union  of  Pachuca,  the  Mantey  offset  is  effectively  used. 
It  is  also  used  on  some  fast-motion  mills.  Some  have  rollers 
inclined  toward  the  center,  like  a  railroad  train  rounding  a  curve; 
others  are  trunnioned  at  a  point  below  the  axle,  so  that  a  portion 
of  the  outward  thrust  is  diverted  to  augment  the  downward 
pressure  of  the  roller  upon  the  die.  In  this  day  a  fast-motion 
roller-mill  that  employs  no  means  to  utilize,  at  least  partially, 
the  centrifugal  thrust  of  the  roller  to  the  crushing  can  hardly  be 
rated  as  high-class  mechanism  because  of  its  wastage  of  force. 
The  Mantey  offset  has  the  axle  of  the  wheel  set  behind  a  diameter 
line  to  which  it  is  parallel,  so  that  in  the  turning  of  the  mill  the 
roller,  not  being  true  with  the  die,  is  more  or  less  shoved  over  it, 
while  at  the  same  time  it  revolves.  When  the  offset  is  properly 
proportioned  to  the  speed  at  which  the  mill  runs  it  is,  as  before 
stated,  thoroughly  successful,  but  as  the  resistance  is  that  of 

156 


ORE-CRUSHING  MACHINERY 


157 


grinding,  it  has  the  objection  of  consumption  of  power  and  metal 
common  to  grinders  in  the  ratio  of  this  action.  When  a  roller  is 
inclined  properly  to  the  speed  at  which  it  is  run  the  thrust  force 
is  entirely  exerted  upon  the  inclined  bed  or  die  without  loss.  A 
vertical  roller,  trunnioned  at  a  point  below  its  axle,  as  in  Fig.  32, 
utilizes  the  centrifugal  thrust  of  the  total  weight  of  the  roller, 
less  that  portion  that  lies  below  a  horizontal  line  through  the 
trunnion,  plus  its  balancing  equivalent  above  said  line.  With 
the  advent  of  faster-motion  mills,  it  has  become  quite  general  to 


FIGS.  31  and  32.  —  Chilean  Mill. 

use  more  than  the  two  wheels  or  rollers  common  to  Spanish- 
American  mills.  If  a  given  weight  is  put  into  two  rollers,  instead 
of  three  or  more,  it  is  simpler  construction,  having  fewer  parts 
and  is  presumably  cheaper,  and  it  is  also  more  convenient  for 
examination  and  repairs.  A  large  roller  presents  a  more  acute 
angle  to  its  bed  than  a  small  one,  for  which  reason  it  is  less  gouged 
by  hard  particles  in  its  path,  consequently  its  proportionate  wear 
is  less.  In  the  accompanying  sketches,  Fig.  31  is  a  plan  of  mill, 
showing  Mantey  offset ;  Fig.  32  is  an  elevation,  showing  the  roller 
trunnioned  below  its  axis. 


PART  IV 
DRIERS  AND  DRYING 


ORE  DRYING 
BY  W.  R.  INGALLS 

(From  the  Pacific  Coast  Miner,  July  11,  1903) 

In  many  metallurgical  processes,  a  preliminary  drying  of  the 
ore  to  be  treated  is  necessary;  especially  is  this  the  case  in  the 
treatment  of  ores  by  processes  wherein  a  fine  crushing  is  required, 
since  not  only  is  it  impossible  to  sift  damp  ore  through  fine  screens, 
but  also  the  capacity  of  the  screens  is  greatly  increased  by  giving 
them  perfectly  dry  ore  at  rather  an  elevated  temperature,  say 
250  deg.  F.  This  is  particularly  important  if  the  ore  be  of  a 
clayey  nature;  ores  of  such  character,  even  if  quite  dry,  lie  dead 
on  the  screens  and  have  a  tendency  to  clog  the  latter  if  the  sifting 
be  done  cold.  When  hot,  however,  such  ores  are  quite  lively  and 
sift  as  well  as  hard,  gritty  ores.  Philip  Argall,  who  has  given 
much  attention  to  this  subject,  illustrates  the  point  by  citing  the 
action  of  wood  ashes;  if  these  are  poured  ever  so  gently  on  dry 
ground  when  quite  hot,  they  will  spread  out  almost  like  water, 
but  if  cold,  they  will  not  spread  to  any  great  extent.  Although 
the  subject  of  ore  drying  is  an  important  one,  it  has  never  been 
treated  upon  to  any  considerable  extent,  so  far  as  I  am  aware. 

If  the  ore  has  to  be  dried,  an  efficient  type  of  apparatus  should 
be  selected.  Probably  there  is  nothing  better  than  the  well- 
constructed  revolving  cylinder  drier  commonly  in  use,  unless  it 
be  a  modern  zigzag  tower  drier;  if  either  be  used,  proper  precau- 
tions should  be  taken  to  avoid  loss  of  fine  ore  in  the  form  of  dust 
carried  off  by  the  chimney  draught;  this  implies  the  installation 
of  a  dust-settling  chamber  between  the  cylinder,  or  tower,  and 
the  chimney.  The  more  valuable  the  ore  under  treatment  the 
more  important  is  attention  to  this  point. 

The  simplest  form  of  drier  is  a  series  of  cast-iron  plates  placed 
over  a  flue  so  that  they  will  be  heated  from  below  by  the  hot 
gases  from  the  fireplace,  each  plate  having  a  flange  at  its  sides 
through  which  adjoining  plates  can  be  bolted  together  if  desired, 
by  which  method  fine  ore  is  prevented  from  sifting  through  the 

161 


162  METALLURGICAL  MILL  CONSTRUCTION 

joints  between  the  plates.  This  form  of  drier  is  easily  adaptable 
to  a  utilization  of  waste  heat  from  other  operations.  It  has  the 
drawback  that,  if  the  plates  be  set  horizontally,  hand  labor  is 
required  in  spreading  and  moving  the  ore,  but  if  the  plates  be 
set  at  an  angle  the  drier  can  be  arranged  so  that  the  dry  ore  will 
slide  off  into  a  conveyor  alongside,  or  directly  to  the  next  opera- 
tion. In  drying  ore  by  indirect  heat,  as  in  this  manner,  the 
capacity  of  the  apparatus  is  determined  largely  by  the  area  of 
the  heating  surface.  In  some  experiments  in  drying  concentrated 
zinc  blende,  which  had  been  sifted  through  a  standard  8-mesh 
sieve,  having  apertures  of  ^  inch,  or  1.59  mm.,  the  ore  con- 
taining 5  per  cent,  moisture,  I  found  that  when  spread  on  an 
iron  plate  in  a  layer  one  inch  thick,  at  a  temperature  below  the 
ignition  point  of  the  ore,  but  above  the  melting  point  of  lead,  it 
could  be  dried  thoroughly  at  the  rate  of  about  25  Ib.  per  square 
foot  of  surface  per  hour.  With  moderate  stirring  it  was  possible 
to  dry  at  the  rate  of  37.5  Ib.  per  square  foot  per  hour,  while  with 
a  well-designed  mechanical  drier  an  efficiency  of  50  Ib.  per  square 
foot  per  hour  would  probably  be  realized.  In  this  case  the  ore 
tested  weighed  125  Ib.  per  cubic  foot,  and  capacity  should  be 
stated  in  terms  of  volume  rather  than  in  terms  of  weight. 

The  zigzag,  or  gravity,  drier  is  a  rational  and  efficient  device, 
but  a  rather  high  belt  elevator  must  generally  be  installed  in 
connection  with  it.  This  form  of  drier  has  been  highly  developed 
in  the  Edison  tower,  which  is  built  in  the  form  of  a  shaft,  3x3  ft. 
or  more  in  area  and  24  ft.  and  upward  in  hight.  These  driers, 
which  are  employed  at  the  magnetic  separating  works  of  the 
New  Jersey  Zinc  Company,  at  Franklin  Furnace,  N.  J.,  occupy 
small  floor  space  at  the  expense  of  hight,  but  in  mill  buildings 
the  latter  is  generally  cheaper  than  the  former.  At  Franklin 
Furnace,  N.  J.,  an  Edison  tower  3x3  ft.  and  24  ft.  in  hight 
dries  ore  of  1.5  in.  and  downward  in  diameter,  containing  4  to 
6  per  cent,  moisture,  at  the  rate  of  500  tons  per  24  hours,  with 
consumption  of  0.12  tons  of  fuel  per  hour,  the  fuel  consisting  of 
one-third  bituminous  coal  and  two-thirds  anthracite  of  buck- 
wheat size.  However,  the  product  from  the  drier  still  contains 
about  1  per  cent,  of  moisture.  In  other  industries,  towers  of 
8x8  ft.  in  area  and  50  ft.  in  hight  are  used. 

Similar  in  principle  to  the  zigzag  driers  are  the  gravity  driers, 
in  which  the  ore  is  heated  as  it  slides  down  a  long  incline. 


DRIERS  AND  DRYING  163 

Another  type  of  drier  which  deserves  attention  is  a  series  of 
troughs  heated  from  below,  or  above,  or  both,  through  which  the 
ore  is  caused  to  travel  by  means  of  endless  screws,  the  latter 
design  being,  in  fact,  an  adaptation  of  the  ordinary  screw-con- 
veyor. Although  the  wear  and  tear  on  such  apparatus  is  rather 
great,  it  is  at  its  best  when  handling  fine  ore,  and  if  the  various 
parts  are  properly  designed,  the  cost  of  repairs  and  renewals 
should  not  be  excessive.  The  movement  of  the  ore  through  a 
trough-conveyor  can  be  effected  by  traveling  rakes  in  the  same 
manner  as  in  a  mechanical  roasting  furnace  or  by  the  push  plates 
of  the  ordinary  scraper  or  drag  conveyor.  Besides  the  cost  of 
repairs  and  renewals,  the  drawbacks  to  making  driers  out  of 
trough  conveyors  are  the  comparatively  large  expense  for  install- 
ing the  amount  of  heating  surface  that  must  be  provided;  and 
the  large  consumption  of  power  required  in  their  operation. 
Driers  of  this  type  have  been  discarded,  in  some  cases,  because 
they  have  failed  to  deliver  a  thoroughly  dry  product,  which 
means,  of  course,  that  a  sufficient  surface  of  the  ore  to  be  dried 
was  not  exposed  under  the  temperature  of  operation.  The 
increasing  use  of  magnetic  separators,  which  must  be  provided 
with  perfectly  dry  ore,  has  caused  the  question  of  driers  to  be- 
come rather  an  important  one.  A  mechanical  development  of 
the  ordinary  plate  drier,  heated  from  below,  consists  in  the  instal- 
lation of  a  circular  hearth  of  cast  iron,  12  to  16  ft.  in  diameter, 
on  which  the  ore  is  fed  near  the  center,  whence  it  is  worked 
peripherally  outward  by  means  of  plows  on  a  rapidly  revolving 
arm,  the  dry  ore  being  finally  discharged  over  the  edge  of  the 
hearth.  This  arrangement  is  much  cheaper  in  first  cost  and, 
also,  in  subsequent  operation  than  any  trough  drier  I  have  ever 
seen. 

The  ordinary  cylindrical  drier  is  too  well  known  to  require 
special  description.  The  cylinder  is  commonly  made  of  steel 
plate,  which  may  be  used  with  or  without  a  brick  lining,  or  of 
cast  iron.  The  loss  in  dust  is  likely  to  be  no  unimportant  matter 
in  drying  fine  ore  in  a  revolving  cylinder,  and  the  more  the  capacity 
of  the  latter  be  increased  by  faster  driving  and  the  harder  the 
firing  (increasing  the  velocity  of  the  combustion  gases  through 
the  cylinder)  the  greater  will  be  the  loss  in  dust.  Hence,  a  cylin- 
drical drier  should  be  of  large  size,  partly  for  the  sake  of  exposing 
a  greater  surface  of  ore  to  the  gas,  thus  permitting  slower  speed, 


164  METALLURGICAL  MILL  CONSTRUCTION 

and  partly  to  reduce  the  velocity  of  the  gas  passing  through  the 
cylinder.'  Both  the  Rothwell  drier,  which  consists  of  a  cylinder 
divided  into  four  quadrants  by  longitudinal  diaphragms,  and  the 
Argall  drier,  which  consists  of  four  small  cylinders,  united  by 
surrounding  rings,  are  logical  improvements  over  the  simple 
cylindrical  drier.  The  Argall  drier  is  made  in  two  sizes,  one  of 
which  has  four  tubes,  each  of  20  in.  diameter  inside  the  lining  and 
17  ft.  in  length,  and  the  other  four  tubes,  each  of  25  in.  diameter 
inside  the  lining  and  25  ft.  in  length.  The  former  has  a  capacity 
of  80  to  100  tons  of  quartzose  ore  per  day,  the  latter  a  capacity  of 
150  to  200  tons  per  day.  In  his  paper  on  "Sampling  and  Dry 
Crushing  in  Colorado,"  Mr.  Argall  gives  some  data  as  to  the 
efficiency  of  these  driers.  At  the  cyanide  mill  at  Leadville,  Colo., 
a  No.  1  four-tube  drier,  with  inclination  of  0.75  in.  to  the  foot, 
making  two  revolutions  per  minute,  dried  70  tons  per  24  hours 
of  soft  clayey  ore,  containing  considerable  talc  and  averaging 
10  per  cent,  moisture,  down  to  1  per  cent,  moisture,  with  a  con- 
sumption of  one  ton  of  coal  of  fairly  good  quality.  At  the  Bessie 
mill,  at  Telluride,  Colo.,  a  No.  2  drier  treated  177  tons  per  24 
hours  of  clayey  ore,  with  consumption  of  2.66  tons  of  coal,  the 
ore  containing  8.06  per  cent,  water  before  drying  and  1.22  per 
cent,  after  drying.  At  the  Leadville  mill  one  pound  of  coal  of 
fair  grade  evaporated  6.3  Ib.  of  water;  at  the  Bessie  mill  1  Ib.  of 
poor  coal  evaporated  4.54  Ib.  of  water;  at  the  mill  of  the  Metallic 
Extraction  Company  at  Cyanide,  Colo.,  1  Ib.  of  good  coal  evapo- 
rated 9  Ib.  of  water.  These  figures  indicate  a  reasonably  high 
utilization  of  the  calorific  power  of  the  coals,  comparing  favorably 
with  the  percentage  of  heat  utilization  in  ordinary  steam  boilers. 


NOTES  ON  ORE  AND  COAL  DRYING  l 

BY  C.  O.  BARTLETT 

(October  17  and  24,  1903) 

Drying  by  direct  heat,  as  in  the  rotary  cylinder  driers,  is 
usually  the  cheapest  method.  Great  care  should  be  taken  in 
the  construction  and  erection  of  all  direct-heat  driers.  All  iron 
parts  should  be  designed  to  allow  for  expansion  and  contraction, 
and  all  settings  and  bearings  should  be  very  substantial.  The 
steel  sheets  of  the  cylinder  should  run  the  entire  length,  and  all 
seams  should  be  longitudinal.  There  should  be  no  cross  seams 
at  all,  since  they  are  liable  to  break. 

The  cost  of  drying  minerals  depends  upon  five  factors,  as 
follows:  (1)  The  percentage  of  moisture  content;  (2)  upon  whether 
or  not  the  mineral  to  be  dried  will  permit  of  the  passage  of  the 
fire-gases  through  it  without  injury;  (3)  upon  whether  or  not 
the  mineral  be  sandy  or  clayey;  (4)  upon  the  ignition  temperature 
of  the  mineral;  (5)  the  degree  of  dryness  to  be  attained.  It  is 
generally  safe  to  estimate  on  evaporating  10  Ib.  of  water  per 
pound  of  coal  burned  in  drying  ores  through  which  the  products 
of  the  fire  can  be  passed.  Most  ores  can  be  dried  by  direct  pas- 
sage of  the  products  of  combustion  over  them,  but  some  fine  clays, 
and  even  some  kinds  of  glass  sand,  will  not  permit  of  this  on 
account  of  danger  of  discoloration.  Silicious  minerals  can  be 
dried  a  good  deal  more  easily  than  clayey  ones.  In  drying  coal 
or  other  material  that  has  a  low  ignition  point,  the  temperature 
must  be  kept  low.  There  is  no  danger,  however,  of  burning  any 
material  containing  a  considerable  percentage  of  water,  and  in 
drying  inflammable  materials  it  is  sometimes  advisable  to  use 
two  driers  in  series,  firing  heavy  on  the  first  one  while  there  is 
plenty  of  moisture,  and  finishing  on  the  second  with  light  firing. 
It  is  very  much  harder  to  dry  ore  down  to  a  moisture  content  of 

i  From  a  paper  read  at  the  American  Mining  Congress  at  Deadwood,  S.  D. 

165 


166  METALLURGICAL  MILL  CONSTRUCTION 

0.5  per  cent,  than  to  2  per  cent.,  and,  generally  speaking,  it  is 
unnecessary  to  go  below  the  latter  figure.1 

The  very  successful  application  of  coal-dust  firing  to  the 
burning  of  cement  in  rotary  kilns  and  the  extensive  use  that  this 
system  is  now  finding  in  the  American  cement  industry  direct 
attention  to  the  means  for  pulverizing  the  coal  to  the  required 
degree  of  fineness.  In  order  to  pulverize  coal  economically  and 
satisfactorily,  it  should  not  contain  more  than  1  per  cent,  moisture. 
The  pulverizing  capacity  of  a  mill  is  nearly  twice  greater  with 
coal  containing  only  1  per  cent,  moisture  than  with  coal  con- 
taining 2  per  cent.  The  moisture  content  must  be  expelled 
from  the  coal  without  causing  the  coal  to  lose  any  of  its  volatile 
combustible.  Two  lots  of  coal  will  rarely  dry  alike,  some  coals 
giving  up  their  moisture  easily  and  freely,  and  others  with  diffi- 
culty. It  appears  that  coals  in  which  the  ash  is  composed  largely 
of  silica  dry  easily  and  thoroughly,  while  those  of  which  the  ash 
is  high  in  lime  or  clay  are  difficult  to  dry.  It  is  very  important 
to  handle  the  coal  in  such  way  that  warm  air  in  large  quantity 
be  brought  in  contact  with  every  particle  of  it,  which  is  best 
accomplished  by  passing  the  current  of  air  from  the  dried  material 
through  that  which  is  wet.  It  is  never  safe  to  pass  the  fire-gases 
through  the  drying  coal.  The  ignition  temperature  of  coals  is 
variable,  as  is  also  the  temperature  at  which  they  will  give  off 
their  volatile  combustible.  In  general,  coal  can  be  safely  deliv- 
ered from  the  drier  at  about  150  deg.  F.  without  loss  of  gas. 
At  225  deg.  F.  there  is  likely  to  be  a  small  loss  of  gas,  and  that 
temperature  cannot  be  recommended  as  good  practice.  It  is 
necessary  to  use  a  fan  blast  to  produce  a  sufficient  current  of  air 
to  carry  off  the  moisture.  This  will  carry  off  3  to  5  per  cent,  of 
coal  dust,  which  should  be  saved  by  passing  the  current  into  a 
brick-dust  settling  chamber,  the  walls  of  which  will  retain  sufficient 
heat  to  prevent  the  moisture  from  condensing. 

1  This  is  to  be  considered  rather  a  high  figure.  Of  course  the  ratio  will 
vary  according  to  the  character  of  the  coal.  —  EDITOR. 


GRINDING  MACHINES  USED  AT  KALGOORLIE ' 
BY  W.  E.  SIMPSON 

(November  14,  1903) 

In  the  Kalgoorlie  district  two  kinds  of  dry-crushers  are  used, 
namely,  ball-mills  and  Griffin  mills.  For  wet  grinding,  flint  mills 
and  Huntington  mills  are  employed.  Ball-mills  have  for  years 
given  every  satisfaction  at  the  Associated,  Kalgurli,  Hannan's 
Star  and  Boulder  Main  Reef  mines,  while  the  Griffin  mills  claim 
supporters  at  the  Perseverance,  South  Kalgurli  and  Great  Boulder 
Proprietary. 

The  Griffin  mill  is  exceedingly  neat  and  compact,  and  occupies 
only  about  one-third  of  the  floor  space  of  a  ball-mill,  but  this  is 
of  small  moment  where  economy,  efficiency,  and  profit  are  the 
chief  matters  to  be  considered. 

In  comparing  the  output  of  a  Griffin  mill  with  that  of  a  ball- 
mill,  it  must  be  recollected  that  the  former  is  fed  with  pieces  no 
bigger  than  walnuts,  while  the  latter  will  take  lumps  as  big  as 
the  fist. 

It  was  found  on  one  occasion  that  75  per  cent,  of  the  ore  fed 
to  the  ball-mills  at  the  Boulder  Main  Reef  was  too  large  to  pass 
through  a  2-in.  ring;  indeed,  3  per  cent,  proved  too  large  to  pass 
through  a  6-in.  ring.  In  spite  of  this,  the  mills  were  each  treating 
33  tons  a  day. 

A  defect  of  the  Griffin  mill  is  its  very  small  screen-area.  The 
pulverized  ore  is  drawn  through  the  meshes  by  the  suction  of  a 
Sturtevant  fan  and  is  caught  by  cyclone  arresters.  It  is  exceed- 
ingly complicated  and  easily  gets  out  of  order,  while  it  possesses 
the  additional  disadvantage  that,  as  the  pendulum  must  revolve 
at  an  enormous  speed,  the  wear  and  tear  is  very  great.  Of  the 
12  Griffin  mills  installed  on  the  Great  Boulder  Proprietary  mine, 

1  Abstract  from  paper  entitled  "  Treatment  of  Telluride  Ores  by  Dry- 
Crushing  and  Roasting  at  Kalgoorlie,  Western  Australia,"  Institution  of 
Mining  and  Metallurgy,  October,  1903. 

167 


168  METALLURGICAL  MILL  CONSTRUCTION 

never  more  than  10  are  running  at  one  time;  the  others  are  always 
under  repair.  The  wearing  parts,  i.e.,  the  roll-tires  and  followers, 
costing  $15.60  and  $10.08  each,  respectively,  require  renewing 
every  eight  days,  while  the  die  rings,  costing  $19.20  each,  and  the 
roll  bodies,  costing  $15.12  each,  last  only  about  six  or  eight 
weeks.  On  the  South  Kalgurli  the  pendulum  shafts  are  replaced 
on  an  average  every  two  months,  at  a  cost  of  about  $48  for  ma- 
terial alone.  Driving-belts  also  suffer  severely,  and  require  to 
be  renewed  twice  a  year.  The  power  required  is  20  indicated 
horse-power  per  mill,  and  the  output  is  1.25  tons  per  hour  of 
running. 

It  is  now  admitted  generally  that  among  the  dry  crushers  the 
ball-mill  has  no  rival  as  regards  output,  low  running  cost,  and 
the  excellence  of  its  finished  product  for  the  subsequent  roasting 
treatment.  The  screen-area  is  enormous,  and  amply  sufficient 
to  secure  the  discharge  of  the  ore  immediately  it  has  been  reduced 
to  the  required  degree  of  fineness,  and  as  the  screens  themselves 
revolve  they  are  subjected  to  a  gentle  internal  scouring,  which 
keeps  them  clean  and  in  proper  trim  for  efficient  working.  The 
cost  of  maintenance  is  exceedingly  moderate,  one  steel  ball, 
weighing  18  lb.,  being  put  into  each  mill  every  day  with  the 
charge  of  ore  in  order  to  make  up  for  the  consumption  of  metal. 
The  other  wearing  parts  are  the  grinding  plates  and  side-liners, 
which  are  replaced  in  complete  sets  every  seven  or  eight  months, 
and  cost  $864  delivered  on  the  mine.  The  driving-belts  on  the 
Boulder  Main  Reef,  which  are  of  camel's-hair,  have  now  been  in 
use  continuously  for  over  four  and  a  half  years,  and  look  as  if 
they  would  still  last  a  long  time. 

Each  mill  makes  exactly  25  revolutions  per  minute,  requires 
about  24  i.  h.  p.,  and  has  an  output  of  over  1J  tons  per  hour. 
The  total  weight  of  the  steel  balls  in  each  mill  varies  from  2240  lb. 
.to  2464  pounds. 

An  examination  of  the  powdered  ore  leaving  the  ball-mills  on 
the  Boulder  Main  Reef,  where  a  screen  of  20  holes  to  the  linear 
inch  is  used,  furnished  interesting  data.  A  sample  assaying 
16  dwt.  per  ton  was  treated  on  a  series  of  brass-wire  sieves.  The 
portion  retained  on  each  was  carefully  weighed  and  assayed 
separately,  with  the  following  results: 


DRIERS  AND  DRYING 


169 


Retained  on 


oz.  dwt.  gr. 


MI    40-mesh  sie 
60 
80 
100 
150 
200 

ve  24.1%  assay. 
9.4  

0  7  20 
.0  11  18 
.0  13  7 

6.2  

6.6  

.0  17  0 

3.2 

0  18  7 

4.2  
46.3.. 

.0  18  7 
.106 

Passing    40 
60 
80 
100 
150 
200 

It  will  thus  be  seen  that  as  regards  value  the  ball-mills  produce 
only  two  qualities;  the  coarse,  largely  made  up  of  hard  particles 
of  quartz,  is  comparatively  poor,  while  the  fine  contains  most 
of  the  gold,  owing  to  the  friability  of  the  sulphides  and  tellurides. 

The  Griffin  mills,  even  with  a  coarser  discharge  screen,  yield 
a  much  finer  product.  For  example,  the  Griffin  mill  at  the  Great 
Boulder  Proprietary  mine,  with  a  15-  to  18-mesh,  produces  an 
impalpable  powder,  of  which  75  per  cent,  will  pass  through  a 
150-sieve.  It  is  claimed  that  the  extra  work  thrown  upon  the 
rock-breakers  in  preparing  for  the  feed  of  the  Griffin  mill  is 
compensated  by  a  corresponding  diminution  of  work  in  the 
Wheeler  pans  in  the  sliming  section  of  the  process;  while  this  is 
admitted,  to  a  certain  extent,  it  cannot  be  denied  that  the  very 
fine  crushing  is  a  distinct  disadvantage  for  the  roasting.  A 
certain  amount  of  grit  is  always  advantageous,  as  it  allows  the 
oxidizing  atmosphere  to  play  more  effectively  in  and  about  the 
fine  sulphurous  particles;  while  at  the  same  time  it  prevents 
that  banking  into  ridges,'  or  packing,  so  noticeable  in  the  treat- 
ment of  the  more  finely  grained  or  floury  material.  Actual 
practice  shows  that  one  5-ft.  Wheeler  pan  will  deal  with  a  daily 
output  of  16.6  tons  from  the  Griffin  mills  and  only  12  tons  from 
the  ball-mills;  but  the  consumption  of  pan  shoes  and  dies  is 
precisely  the  same,  being  1.8  Ib.  per  ton  of  original  ore  in  either 
case. 

One  other  point  in  favor  of  the  ball-mill  is  that  when,  as  not 
infrequently  happens,  a  dynamite  cartridge  is  carelessly  shoveled 
up  in  the  mine  and  sent  up  with  the  ore,  its  explosion  does  little 
or  no  damage  to  the  ball-mill  because  of  the  great  space  available 
in  which  to  expend  its  energy.  This  is  not  the  case  with  the  com- 
pact Griffin  mill,  where  the  explosion  is  confined  and  often  blows 
the  bottom  to  pieces.  The  expense  incurred  in  repairing  the 
results  of  an  accident  of  this  kind  amounted  formerly  to  $192  to 
$336;  but  these  figures  are  now  considerably  reduced  through 


170  METALLURGICAL  MILL  CONSTRUCTION 

the  substitution  of  false  bottoms  of  sheet  iron  for  the  heavy 
castings.  However,  even  now  the  cost  of  repairs  is  heavy,  be- 
sides which,  time  is  lost  and  the  mill  is  lying  idle  while  the  damage 
is  being  put  right. 

Another  type  of  pulverizer,  much  favored  on  this  field,  is  the 
flint  mill.  It  is  a  hollow  revolving  steel  cylinder,  16  to  20  ft.  in 
length  and  4  or  5  ft.  in  diameter,  and  closed  at  both  ends  except 
for  a  small  central  opening  in  each.  It  is  lined  completely  with 
cast-iron  or  steel  plates  j  to  1J  in.  thick,  and  when  in  operation 
is  partially  filled  with  a  charge  of  hard  flint  nodules.  The  sand  is 
forced  from  the  nozzle  of  a  spit zkasten  through  the  central  opening 
in  the  receiving  end,  is  ground  in  the  mill,  and  escapes  as  slime 
at  the  discharge  orifice.  One  flint  mill  is  sufficient  for  a  2000-ton 
per  month  plant,  using  a  30-mesh  wire  screen,  and  the  work  is 
done  so  efficiently  that  99  per  cent.,  or  practically  the  whole,  of 
the  finished  product  will  pass  through  a  sieve  of  200  holes  to  the 
linear  inch. 

A  complete  set  of  liners  weighs  about  4  tons,  lasts  from  7  to 
10  months,  and  costs  $384  on  the  spot. 

The  working  charge  of  flints  ranges  from  4  to  6  tons,  and 
about  1  cwt.  of  flints  is  consumed  in  grinding  100  tons  fine  enough 
to  pass  through  a  wire  screen  with  30  holes  per  linear  inch.  Each 
mill  consumes  from  18  horse-power  to  35  horse-power,  according 
to  size,  makes  30  revolutions  per  minute,  and,  when  working 
efficiently,  emits  a  low,  dull  note  or  roar  easily  recognized  by  an 
experienced  attendant. 

The  function  of  a  flint  mill  is  to  pulverize,  and  as  such  it  is 
at  present  unsurpassed,  while  the  pan  (which  is  also  used  in  the 
treatment  at  Kalgoorlie)  has  not  only  to  grind,  but  also  to 
amalgamate. 

Huntington  mills  have  been  tried  for  pulverizing  the  roasted 
ore,  but  the  ever-present  plaster-of-paris  soon  encrusts  and 
enamels  all  the  exposed  ironwork,  the  fine  mill  screens  rapidly 
become  choked,  and  further  work  is  impossible. 


PART  V 
CONVEYORS  AND  ELEVATORS 


MECHANICAL  CONVEYORS 
BY  W.  R.  INGALLS 

(April  21.  1904) 

Mechanical  conveyors,  of  which  there  is  a  great  variety,  may 
be  classified  as  of  (1)  the  push  or  drag  type,  and  (2)  the  carrying 
type.  In  the  former,  the  material  is  pushed  or  dragged  forward 
in  a  trough.  In  the  latter  type,  it  is  continuously  carried  forward 
on  a  belt,  or  in  a  series  of  connected  pans  or  buckets,  which  take 
the  place  of  a  belt.  In  a  horizontal  conveyor  the  only  mechanical 
work  to  be  done  consists  in  the  overcoming  of  friction.  It  is 
obvious,  therefore,  that  a  well-mounted  belt  or  series  of  buckets 
can  be  moved  with  less  friction  and  therefore  requires  less  power 
than  any  form  of  conveyor  in  which  the  material  has  to  be  pushed 
or  dragged  forward. 

All  of  these  conveyors  are  used  in  practice,  some  of  them 
extensively.  Some  of  them  are  extremely  efficient  machines; 
others  have  very  little  to  commend,  yet  are  useful  for  some 
special  purposes  because  of  limitations  in  the  application  of 
better  types.  The  special  form  of  conveyor  must  always  be 
chosen  with  view  to  the  work  that  is  to  be  done.  In  this  article, 
I  have  reference  only  to  the  use  of  conveyors  for  the  transporta- 
tion of  ore  and  other  mineral  substances.  There  is  a  dearth  of 
practical  information  on  this  subject;  even  the  manufacturers 
appear  to  lack  a  good  deal  of  important  data.  It  is  obviously  a 
subject  in  which  experiences  may  differ  widely  under  varying 
conditions. 

PUSH  OB  DRAG  CONVEYORS 

Among  the  conveyors  of  this  type  are  the  screw,  the  scraper, 
and  the  reciprocating.  All  of  them  have  the  advantage  that 
material  can  be  discharged,  without  complicated  machinery,  at 
any  desired  point,  which  makes  them  especially  useful  for  the 
filling  of  a  series  of  bins. 

173 


174  METALLURGICAL  MILL  CONSTRUCTION 

Screw-Conveyor.  —  The  screw-conveyor  is  one  of  the  oldest 
of  conveying  devices.  Also,  it  is  perhaps  one  of  the  most  inferior. 
The  screw-conveyor  consists  commonly  of  a  trough  of  iron  or 
steel,  with  semi-cylindrical  bottom,  in  which  is  turned  an  endless 
screw,  composed  of  a  shaft,  solid  or  hollow,  and  a  spiral  of  steel 
or  cast  iron.  The  shaft  is  supported  in  boxes  at  each  end  of  the 
trough,  and  by  intermediate  hangers  in  long  conveyors,  and  is 
driven  by  pulley,  gear,  or  sprocket  wheel.  The  shaft  is  generally 
made  in  sections,  which  may  be  united  in  any  suitable  manner, 
though  certain  devices  are  much  better  than  others.  The  spiral 
is  ordinarily  of  8-in.,  10-in.,  or  12-in.  diameter.  In  transporting 
ore  it  is  inadvisable  to  turn  a  9-in.  or  10-in.  screw  at  more  than 
50  to  75  revolutions  per  minute,  since  a  higher  speed  is  apt  to 
throw  material  out  of  the  trough  and  produce  too  much  dust. 
Obviously,  the  speed  should  dimmish  as  the  diameter  of  the 
screw  increases. 

The  capacity  of  a  screw-conveyor  depends  upon  the  diameter 
and  pitch  of  the  screw,  its  speed  of  revolution,  and  the  specific 
gravity  of  the  material  to  be  transported.  One  manufacturer 
gives  the  capacity  of  a  6-in.  screw,  run  at  100  revolutions  per 
minute,  at  3  tons  per  hour;  of  a  9-in.  screw  at  70  revolutions  per 
minute,  8  tons  per  hour;  and  of  a  12-in.  screw  at  50  revolutions, 
15  tons  per  hour.  It  is  presumable  that  these  figures  for  capacity 
refer  to  quartzose  ore,  which  may  be  taken  as  weighing  100  Ib. 
per  cu.  ft.  Another  manufacturer  estimates  the  capacity  of  a 
5J-in.  screw  at  120  revolutions,  42  cu.  ft.  per  hour;  7J-in.  at  110 
revolutions,  71  cu.  ft.;  9J-in.,  at  100  revolutions,  141  cu.  ft.; 
llf-in.,  at  80  revolutions,  247  cu.  ft.  It  is  quite  right  to  state 
these  data  in  cubic  feet,  instead  of  by  weight,  but  the  speeds 
given  are  too  high  for  good  practice.  However,  the  capacities 
appear  to  be  stated  moderately,  notwithstanding.  On  the  basis 
of  material  weighing  100  Ib.  per  cu.  ft.,  the  capacity  of  the  5J-in. 
screw  would  be  2.1  tons  per  hour;  of  the  7J-in.  screw,  3.55  tons; 
of  the  9f-in.  screw,  7.05  tons;  and  of  the  llf-in.  screw,  12.35  tons. 
The  figures  of  either  of  these  manufacturers  seem  to  be  on  the 
safe  side  as  to  capacity,  since  a  9-in.  conveyor  run  at  70  revolu- 
tions per  minute  will  certainly  transport  10  tons  per  hour  of  ore 
weighing  150  Ib.  per  cu.  ft.,  or  6§  tons  of  ore  weighing  100  Ib. 
per  cu.  ft. 

Ideas  as  to  the  power  required  to  operate  a  screw-conveyor 


CONVEYORS  AND  ELEVATORS  175 

are  less  definite.  In  the  transportation  of  any  substance  hori- 
zontally, friction  is  the  only  element  which  has  to  be  overcome, 
not  only  the  friction  of  the  material  itself,  but  also  that  of  the 
mechanism.  It  is  evident,  therefore,  that  the  power  required  is 
a  function  of  the  weight  of  the  material,  the  distance  to  which  to 
be  carried  and  the  speed,  plus  the  similar  factors  for  the  mechan- 
ism. One  manufacturer  states  that  a  5J-in.  screw  run  at  120 
revolutions  per  minute  requires  0.5  horse-power  per  33  ft.  of 
length;  a  7|~in.  screw  at  110  revolutions,  6.75  horse-power;  and 
a  9J-in.  screw  at  100  revolutions,  1  horse-power.  These  figures 
are  rather  lower  than  practice  indicates,  and  would  appear  to 
correspond  more  closely  to  the  power  required  to  drive  the  con- 
veyor empty  than  full.  Another  manufacturer  gives  the  formula, 
H.  P.  =  WL  -?-  3  X  33,000,  in  which  W  is  the  weight  in  pounds 
of  the  material  to  be  carried  per  minute,  and  L  the  distance  in 
feet  to  which  it  is  to  be  carried.  According  to  this,  the  power 
required  to  carry  10  tons  of  ore  100  ft.  per  hour  would  be  only 
0.33  horse-power,  which  of  course  is  absurd,  since  it  would  require 
far  more  power  than  that  to  run  the  conveyor  empty.  A  9-in. 
screw  conveying  that  quantity  of  material  would  probably  re- 
quire 4  to  5  horse-power.  The  formula  should  evidently  be 
expressed  as  H.  P.  =[WL  -=-  (3  X  33,000)]  +  FL,  in  which  F 
stands  for  the  power  required  to  turn  the  screw  itself  at  a  specified 
speed.  The  screw  is  wasteful  of  power,  because  not  only  is  the 
ore  pushed  through  the  trough  as  in  the  scraper-conveyor,  but 
also  the  screw  presents  a  greatly  increased  frictional  surface, 
while  it  is  subject  to  all  the  frictional  resistance  of  a  poorly 
supported  and  carelessly  attended  line  of  shafting,  running  in 
grit  all  the  time. 

The  screw-conveyor  is  the  cheapest  of  all  conveyors  to  install. 
A  9-in.  screw,  100  ft.  long,  ought  to  be  put  up  for  about  $300. 
On  the  other  hand,  all  of  its  parts  are  subject  to  heavy  wear, 
and  repairs  and  renewals  may  easily  amount  to  100  per  cent, 
per  annum,  this  depending  upon  the  work  required  of  it.  There 
are  some  cases  wherein  it  is  advantageous  to  use  a  screw,  not- 
withstanding its  serious  drawbacks.  They  are  at  their  best  when 
used  for  finely  crushed  and  dry  ore.  They  are  more  troublesome 
with  wet,  clayey  ores,  and  are  quite  unsuitable  for  coarse  ores. 
A  very  long  screw  is  apt  to  be  a  nuisance  anyway.  A  short 
screw  often  makes  a  good  feeding  device.  The  screw-conveyor 


176  METALLURGICAL  MILL  CONSTRUCTION 

with  externally  heated  trough  has  been  proposed  as  a  drying 
and  roasting  furnace.  It  has  been  used  occasionally  for  the 
former  purpose,  but  not  for  the  latter.  Neither  arrangement 
commends  itself. 

Rotary  Conveyor.  —  The  screw-conveyor  is  often  referred  to 
as  a  spiral  conveyor.  Another  form  of  spiral  conveyor  consists 
of  a  cylinder  with  an  interior  spiral,  the  cylinder  being  supported 
on  rollers  and  revolving  like  a  cylindrical  roasting  furnace. 
Conveyors  of  this  form  are  seldom  used.  They  would  appear  to 
be  costly,  clumsy,  and  difficult  to  repair,  while  material  can  only 
be  fed  at  one  end  and  discharged  at  the  other  end,  which  in 
adaptability  would  make  it  the  least  advantageous  of  all  con- 
veyors.1 If  the  cylinder  be  set  on  an  incline,  or  if  it  have  a 
taper,  of  course  no  interior  spiral  is  necessary.  The  cylindrical 
drier  and  several  forms  of  roasting  furnaces  are  really  forms  of 
this  type  of  conveyor,  just  as  other  mechanical  drying  and  roasting 
furnaces  embody  the  principle  of  the  scraper-conveyor.  Roasting 
cylinders  as  long  as  60  ft.  are  used  in  Europe,  and  cement  kilns 
as  long  as  120  ft.  are  used  in  the  United  States. 

Scraper  Conveyor.  —  The  scraper-conveyor  consists  essentially 
of  a  trough  in  which  the  ore  is  dragged  forward  by  a  series  of 
transverse  push-plates  called  flights.  The  method  of  connecting 
the  push-plates  is  subject  to  a  large  number  of  modifications. 
Thus  there  is  the  continuous  cable,  dragging  circular  flights 
through  a  V-shaped  or  semi-cylindrical  trough,  and  the  monobar 
conveyor,  in  which  the  flights  are  carried  by  a  series  of  single 
linked  bars.  One  of  the  commonest  forms  of  this  type  of  con- 
veyor is,  however,  the  double  link-belt  chain,  supported  on  rollers, 
wheels  or  sliding  shoes,  which  run  on  rails  at  each  side  of  the 

1  Morris  M.  Green,  in  the  Engineering  and  Mining  Journal,  May  26,  1904, 
criticized  the  statement  that "  material  can  only  be  fed  at  one  end,"  saying  that 
he  knew  of  one  conveyor  of  this  sort  which  has  five  inlets,  receiving  material 
discharged  from  as  many  furnaces.  This  type  of  conveyor  may  be  costly,  but 
such  cost  might  be  justified  by  advantages,  under  certain  circumstances.  As 
a  cooling  conveyor,  it  is  remarkably  successful  where  materials  like  cement 
clinker  are  to  be  conveyed  and  cooled  simultaneously,  without  loss  of  objec- 
tionable dust  into  the  atmosphere  of  a  mill,  where  it  can  embarrass  workmen. 
Material  in  a  rotary  conveyor  can  be  cooled  by  drawing  air  through  the  con- 
veyor tube,  and  the  hot  air  can  be  utilized.  Also  water  can  be  sprinkled  on 
the  conveyor's  exterior,  where  the  nature  of  the  material  does  not  allow  direct 
contact  with  water. 


CONVEYORS  AND  ELEVATORS  177 

trough,  carrying  the  flights  between  them.  This  is  known  as  the 
suspended-flight  conveyor.  The  chains  pass  over  sprockets  at 
each  end  of  the  conveyor  and  return  on  overhead  rails.  The 
sprockets  at  one  end  are  keyed  on  the  driving-shaft,  while  those 
at  the  other  end  are  carried  in  boxes  which  can  be  adjusted  to 
take  up  the  slack  in  the  chains.  The  monobar  conveyor  can  be 
constructed  so  as  to  make  a  bend  in  the  horizontal  plane,  or  even 
make  the  complete  return  circuit. 

The  scraper-conveyors  have  the  advantage  that  they  can  be 
arranged  to  be  fed  or  to  discharge  at  any  point.  They  have  the 
disadvantages  of  involving  a  good  many  wearing  parts  and 
requiring  considerable  power  to  drive.  The  Link-Belt  Engineer- 
ing Company  gives  the  following  formula  for  power: 

H.  P.  =  (ATL  +  BWS)  -i-  1000, 

in  which  A  and  B  are  constants  depending  on  angle  of  inclination 
from  the  horizontal,  T  is  the  tons  per  hour  to  be  conveyed,  L 
the  length  of  the  conveyor  in  feet,  center  to  center,  W  the  weight 
in  pounds  of  chains,  flights,  and  shoes,  and  S  the  speed  in  feet 
per  minute.  For  horizontal  runs,  A  =  0.343  and  B  =  0.01. 
According  to  this  formula,  the  power  required  to  move  10  tons 
of  ore  per  hour  the  distance  of  100  ft.  would  be  3.5  horse-power, 
but  I  should  hesitate  to  reckon  so  low.  Anyway,  it  always 
requires  more  power  to  start  a  conveyor  than  to  operate  it,  and 
therefore  a  larger  motor  should  be  provided.  Scraper-conveyors 
are  usually  operated  at  speeds  of  about  100  ft.  per  minute.  The 
weight  of  the  chains,  scrapers,  wheels  and  axles,  or  rollers,  amounts 
to  about  30  to  35  Ib.  per  foot,  center  to  center,  for  a  10-in.  or 
12-in.  suspended-flight  conveyor,  which  at  100  ft.  travel  per 
minute  will  have  capacity  for  moving  about  10  tons  per  hour  of 
ore  weighing  150  Ib.  per  cu.  ft.  The  cost  of  a  suspended-flight 
conveyor  100  ft.  long,  installed,  will  come  to  about  $450. 

The  capacity  of  a  scraper-conveyor  depends  upon  the  width 
of  the  trough,  the  speed  of  the  chain,  the  volume  of  the  ore,  and 
the  frequency  of  the  flights.  The  flights  are  commonly  set  16  in., 
18  in.,  or  24  in.  apart.  Obviously,  the  flights  will  not  push  the 
ore  ahead  in  an  even  sheet,  but  will  crowd  it  up  into  little  heaps, 
a  succession  of  which  will  be  moving  through  the  trough.  There- 
fore, the  more  frequent  the  flights,  the  greater  the  capacity  of 
the  conveyor.  The  suspended-flight  conveyor  is  superior  to 


178  METALLURGICAL  MILL  CONSTRUCTION 

other  forms;  it  requires  about  20  per  cent,  less  power  than  the 
simple  drag,  runs  more  smoothly  and  is  not  so  noisy.  The  point 
of  special  weakness  in  these  conveyors  is  the  chains,  the  breakage 
of  which  is  likely  to  cause  costly  and  vexatious  delays.  The 
monobar  is  better  than  the  chains;  the  latter,  if  used,  should  be 
provided  of  greater  strength  than  is  frequently  the  case.  The 
scraper-conveyor  gives  the  best  results  with  fine  ore  and  moderate 
lengths.  Many  examples  of  large  and  long  installations  for  the 
handling  of  lump  ore,  coal  and  rock  are  to  be  seen.  They  are 
very  noisy  and  are  subject  to  frequent  breakdowns. 

Reciprocating  Conveyor.  —  The  reciprocating  conveyor  is  a 
new  modification  of  the  scraper-conveyor,  which  is  finding  con- 
siderable favor.1  In  this  the  ore  is  pushed  forward  in  a  trough 
by  a  series  of  flights  which  are  hinged  at  regular  intervals  to  a 
ladder-like  frame,  composed  of  a  pair  of  channel  beams  joined  by 
suitable  cross-bars  and  mounted  on  rollers.  This  frame  is  given 
a  reciprocating  motion  by  a  crank  mechanism,  which  can  be 
placed  at  any  convenient  point.  In  another  form,  the  flights  are 
fixed  to  a  reciprocating  rod,  such  as  an  iron  pipe  of  suitable 
strength,  which  is  supported  by  wheels  and  axles.  In  either  case, 
the  flights  are  so  hinged  that  in  their  forward  motion  they  bear 
against  stops,  and  push  the  material  along,  while  in  the  backward 
motion  they  return  to  the  starting  point  by  dragging  back  over 
the  top  of  the  material.  In  this  way  the  ore  is  literally  shoveled 
forward,  stroke  by  stroke. 

In  the  gold  mills  at  Kalgoorlie,  Western  Australia,  the  recip- 
rocating conveyor  has  superseded  all  others,  being  commended 
for  its  simplicity  and  low  cost  for  repairs.  As  used  there  it 
consists  of  a  semicircular  trough  about  60  ft.  long,  provided  with 
a  ladder-like  frame,  with  blades  hanging  from  the  rungs,  which 
is  made  to  move  horizontally  to  and  fro  on  rollers.  The  blades 
are  free  to  swing  in  one  direction,  but  are  prevented  by  a  stop 
from  swinging  further  back  than  the  perpendicular.  When  the 
ladder  is  traveling  forward,  each  blade  hangs  vertically,  and 

1  A  correspondent  writing  in  the  Engineering  and  Mining  Journal,  of  May 
5, 1904,  criticizes  the  statement  that  the  reciprocating  conveyor  is  a  modifica- 
tion of  the  scraper-conveyor.  This  is,  however,  a  mere  matter  of  classification. 
He  remarks  further  that  the  late  Eckley  B.  Coxe  designed  and  installed  a 
reciprocating  conveyor  at  an  anthracite  breaker  some  time  in  the  80's  —  about 
1886.  It  was  not  a  success  economically,  because  of  the  cost  of  repairs  and 
renewals. 


CONVEYORS  AND  ELEVATORS 


179 


pushes  a  little  heap  of  ore  before  it  for  a  distance  of  20  in.,  the 
length  of  the  stroke.  (See  Fig.  33.)  On  the  return  stroke  the 
blades,  being  free  to  swing,  slip  over  the  tops  of  the  little  heaps, 
and  on  the  completion  of  the  stroke  resume  their  original  vertical 
position.  (See  Fig.  34.) 


FIG.  33.  —  Push  Conveyor,  Forward  Stroke. 

The  reciprocating  conveyor  has  these  advantages:  It  can  be 
fed  and  discharged  at  any  point;  it  occupies  less  hight  than  the 
chain  scraper-conveyor;  and  all  of  its  wearing  parts,  which 


0        1       2       3        1        6       o       7        89      10  Feet 

FIG.  34.  —  Push  Conveyor,  Backward  Stroke. 

anyway  are  comparatively  few,  are  outside  of  the  grit,  save  the 
flights  themselves  and  the  trough.  On  the  other  hand,  it  is 
uneconomical  of  power,  owing  to  the  frequency  with  which 
motion  is  reversed.  At  every  stroke  the  inertia  of  the  entire 
lot  of  ore  in  the  trough  has  to  be  overcome,  and  this  will  probably 


180  METALLURGICAL  MILL  CONSTRUCTION 

limit  the  usefulness  of  this  type  of  conveyor  to  a  comparatively 
moderate  length.  Moreover,  they  are  obviously  inapplicable  to 
conveying  materials  containing  lumps.  They  are  considerably 
more  costly  than  the  ordinary  scraper-conveyor,  the  cost  varying 
according  to  the  details  of  manufacture.  Thus,  to  install  a  re- 
ciprocating conveyor  100  ft.  long,  capable  of  transporting  10  tons 
per  hour  of  ore  weighing  150  Ib.  per  cu.  ft.,  would  cost  from  $700 
to  $1200  (actual  quotations,  with  an  allowance  for  cost  of  instal- 
lation). A  15-horse-power  motor  should  be  provided  to  drive. 
The  capacity  of  this  form  of  conveyor  is  determined  by  substan- 
tially the  same  factors  as  in  the  case  of  the  scraper-conveyor. 

Another  form  of  reciprocating  conveyor  consists  of  a  light 
trough,  supported  or  suspended  in  a  suitable  manner,  to  which 
a  to-and-fro  movement  is  imparted  by  suitable  mechanism. 
This  form  of  conveyor  is  not  in  general  use,  but  I  have  seen  it 
employed  with  good  success  for  transports  of  several  hundred 
feet,  the  entire  installation  being  of  the  simplest  construction. 
Obviously,  however,  it  is  suitable  only  for  fine,  dry  material,  or 
else  a  loose  pulp.  In  either  case,  the  forward  travel  of  the  material 
will  depend  upon  the  slope  of  the  trough  and  the  length  and 
number  of  the  jerks.  The  Wilfley  conveyor,  which  is  of  this 
type,  is  used  for  the  transport  of  wet  concentrates,  the  motion  of 
the  trough  being  given  by  the  same  mechanism  that  is  used  for 
the  Wilfley  table.  A  recently  patented  reciprocating  trough- 
conveyor  has  the  bottom  of  the  trough  made  in  a  serrated  form, 
so  that  at  each  jerk  the  material  goes  over  a  ledge  and  therefore 
attains  a  positive  forward  movement. 

CARRYING  CONVEYORS 

The  conveyors  of  this  type  consist  substantially  of  an  endless 
belt,  or  a  continuous  chain  of  pans  or  buckets.  There  are  numer- 
ous modifications  of  both  forms. 

Belt  Conveyor.  —  The  belt  conveyor  is  essentially  a  band  sup- 
ported on  idlers  and  running  over  pulleys  at  either  end,  by  one 
of  which  it  is  driven,  A  suitable  arrangement  at  the  other  end 
serves  to  take  up  slack  and  keep  the  belt  tight.  The  simplest 
conveyor  of  this  type  has  a  flat  belt,  which  has  to  be  quite  wide  in 
order  to  prevent  material  from  spilling  off.  To  obviate  this,  the 
belt  is  concaved,  and  to  reduce  the  wear  of  the  belt  by  being  thus 
flexed  it  is  manufactured  in  various  ways.  There  is  also  a  great 


CONVEYORS  AND  ELEVATORS  181 

variety  in  the  composition  of  rubber  employed  and  in  the  design 
of  the  supporting  rollers.  Rarely,  a  flat  belt  with  side  rims  is 
run  over  plain  rollers. 

Irrespective  of  these  modifications  in  design  and  construction, 
the  belt  conveyor  is  for  many  purposes  the  most  efficient  of  all 
conveyors.  It  requires  the  least  power  to  drive,  save  for  the 
highly  developed  forms  of  continuous  bucket  conveyors;  its  first 
cost  is  moderate,  and  the  expense  for  repairs  and  renewals  is  less 
than  for  any  other  form  of  approximately  equal  first  cost.  It  is 
adapted  to  a  great  variety  of  uses,  carrying  ore  up  considerable 
inclines  and  at  changes  of  angle,  and  has  great  capacity.  By 
means  of  a  tripper,  which  has  been  greatly  improved  in  design, 
discharge  can  be  effected  from  the  belt  at  any  desired  point.  It 
is  possible,  moreover,  where  electric  power  is  available,  to  install  a 
movable  conveyor,  run  by  a  self-contained  motor,  and  to  cause  the 
belt  to  discharge  over  the  end  into  any  one  of  a  series  of  bins,  by 
moving  it  forward  or  back;  and  the  direction  of  the  belt  travel 
can  be  reversed.  Thus,  a  line  of  bins  200  ft.  long  can  be  filled 
by  a  conveyor  of  a  little  more  than  half  that  length,  the  feed 
being  received  midway  in  the  line  of  the  bins.  Similarly  such 
self-contained  conveyors  can:  be  constructed  in  portable  form 
and  used  for  work  about  the  yard,  such  as  the  loading  of  railway 
cars.  These  are  things  which  cannot  be  done  so  conveniently 
with  any  other  type  of  conveyor.  Moreover,  this  can  be  used  as 
a  sorting  belt  at  the  same  time  as  a  carrying  belt,  and  in  taking 
ore  to  breakers  and  rolls  a  magnet  can  be  set  over  the  belt  to  pick 
out  drill  points  and  other  undesirable  pieces  of  steel  and  iron. 

The  rubber  belt  is  quite  durable  and  it  may  be  reinforced  on 
the  wearing  side  by  an  extra  layer  of  rubber,  like  elevator  belts. 
It  is,  however,  unsuitable  for  carrying  ore  from  driers,  etc.,  which 
is  of  such  temperature  as  to  affect  the  rubber.  The  limit  of 
rubber  belting  in  this  respect  is  soon  reached  (it  would  be  unsafe 
to  attempt  to  carry  ore  so  hot  as  150  deg.  C.),  but  in  such  cases 
the  Leviathan  or  Gandy  belts  may  be  substituted.  Such  cotton- 
duck  belts  are,  however,  less  durable  against  abrasion  than  the 
rubber. 

The  capacity  of  a  belt  conveyor  depends  upon  the  width  and 
speed  of  the  belt  and  the  weight  of  the  material  to  be  carried. 
If  the  belt  is  troughed  it  is  safe  to  estimate  that  the  load  will 
cover  one-half  of  the  total  width  of  the  belt,  and  that  the  depth 


182  METALLURGICAL  MILL  CONSTRUCTION 

in  the  center  will  be  one-quarter  of  its  own  width.  The  cross- 
sectional  area  of  the  load  (which  may  be  considered  as  an  inverted 
triangle)  multiplied  by  12  will  give  the  number  of  cubic  inches  of 
material  per  running  foot  of  length,  and  from  the  weight  of  the 
material  and  speed  of  the  belt  the  capacity  may  easily  be  calcu- 
lated, but  an  allowance  must  be  made  for  irregularity  in  feeding. 
A  flat  belt  will  carry  only  about  one-third  as  much  as  a  troughed 
one.1 

A  belt  speed  of  about  300  ft.  per  minute  is  commonly  used, 
but  450  ft.  per  minute  is  not  excessive;  belts  have  been  observed 
to  run  smoothly  at  a  speed  as  high  as  900  ft.  per  minute,  but  the 
wear  on  both  the  belt  and  the  idlers  was  then  excessive,  and  so 
high  a  speed  in  no  way  is  to  be  recommended. 

A  troughed  12-in.  belt,  run  at  100  ft.  per  minute,  is  able  to 
carry  187.5  cu.  ft.  per  hour,  or  14  tons  of  ore  weighing  150  Ib. 
per  cu.  ft.,  which  would  be  ample  for  the  duty  that  I  have  assumed 
for  other  conveyors  in  this  article,  viz.,  the  transport  of  10  tons 
per  hour.  The  cost  of  such  a  conveyor  installed  would  be  about 
$600  for  a  length  of  100  ft.  It  would  require  less  than  one 
horse-power  to  drive,  assuming  it  to  be  properly  installed.  No 
general  rule  can  be  given  for  estimating  the  power  required  to 
drive  a  belt  conveyor,  which  depends  largely  on  the  arrangement 
of  the  idlers.  If  they  are  too  far  apart  the  belt  will  sag  down  be- 
tween them,  increasing  the  load;  if  they  are  too  near  together  the 
frictional  resistance  is  increased.  The  greatest  item  of  repairs  in 
connection  with  a  belt  conveyor  is  the  replacement  of  the  belt, 
which  is  the  most  costly  single  piece  of  the  apparatus.  If  the 
belt  lasts  five  years  the  cost  of  repairs  will  come  to  about  12.5 
per  cent,  per  annum;  a  belt  life  of  only  2.5  years  would  mean  a 
repair  cost  of  about  20  per  cent,  per  annum.  In  a  certain  large 
works  where  a  good  many  belt  conveyors  are  employed  the  actual 
expense  for  repairs  is  not  much  more  than  12.5  per  cent,  per 
annum. 

It  is  to  be  remarked  that  the  belt  conveyor  is  a  type  of  great 
capacity,  and  for  the  transportation  of  large  quantities  of  mate- 
rial, for  which  it  is  especially  adapted,  it  appears  much  more 
favorably  as  regards  first  cost,  operating  cost  and  maintenance 
than  for  the  transportation  of  the  relatively  small  quantity  of 

Thomas  Robins,  Jr.,  Transactions  American  Institute  of  Mining  Engi- 
neer, XXVI,  pp.  78-97. 


CONVEYORS  AND  ELEVATORS  183 

material  which  for  purpose  of  comparison  has  been  assumed  in 
this  paper. 

Continuous  Bucket  Conveyors,  —  The  pan  and  bucket  con- 
veyors consist  essentially  of  an  endless  chain  of  overlapping  pans 
and  buckets,  which  may  be  arranged  in  a  great  variety  of  ways. 
One  of  the  simplest  is  the  endless  traveling-trough  conveyor 
(referred  to  also  as  the  open-trough  conveyor  and  apron  con- 
veyor), consisting  of  a  series  of  overlapping  sections  of  light 
sheet-steel  trough,  which  are  secured  on  the  under-side  to  a  heavy 
link-belt  chain  (or  to  a  pair  of  chains);  the  chain  passes  over  a 
sprocket  at  each  end  of  the  conveyor  and  the  pans  are  supported 
on  rollers  attached  to  the  frame.  These  conveyors  are  consid- 
erably more  expensive  than  the  belt  conveyors.  The  first  cost 
of  a  12-in.  conveyor  of  this  type,  which  would  have  capacity  for 
10  tons  of  ore  per  hour,  would  be  in  the  neighborhood  of  $11@$12 
per  foot,  installed.  Ordinarily  they  have  the  disadvantage  of 
being  able  to  discharge  only  at  the  end,  where  the  pans  pass  over 
the  tail  sprocket  (although,  in  the  forms  wherein  the  pans  are 
carried  between  a  pair  of  chains,  they  can  be  arranged  to  dump 
at  intermediate  points  by  having  a  dip  in  the  rails),  and  in  this 
respect  are  of  more  limited  application  than  the  belt  conveyors, 
but  on  the  other  hand  they  are  suitable  for  conveying  hot  material 
or  substances  that  would  injure  a  belt.  Conveyors  of  this  type, 
of  heavy  construction,  are  used  at  various  places  for  the  transpor- 
tation of  hot  slag,  and  when  properly  installed  give  good  service. 
It  is  only  a  little  step  further  to  the  casting  and  conveying  machines 
for  pig  iron  and  other  metals. 

For  the  transportation  of  ore  and  coal  and  such  substances 
the  highest  development  in  conveyors  of  this  class  is  to  be  seen 
in  the  Hunt  and  the  McCaslin  and  similar  designs.  These  consist 
of  a  series  of  deep  buckets,  which  overlap  so  as  to  prevent  spilling 
of  material  between  them  while  being  fed,  carried  on  wheels 
running  on  rails.  The  whole  contrivance  is  virtually  a  chain,  or 
endless  train,  of  small  cars.  In  the  Hunt  conveyor,  the  train  is 
moved  by  an  engine  having  an  arrangement  of  gears  and  pawls 
so  disposed  as  to  engage  the  cross-rods  or  rivets  connecting  links 
in  the  chain  to  which  the  buckets  are  fixed.  This  gives  a  con- 
tinuous pushing  action  and  an  even  and  practically  noiseless 
motion  of  the  conveyor.  The  buckets  may  be  discharged  at  any 
desirable  point  by  adjusting  a  simple  lever  which  engages  with 


184  METALLURGICAL  MILL  CONSTRUCTION 

each  bucket  and  turns  it  completely  over.  The  buckets  may 
also  be  fed  at  any  point ;  this  is  done  usually  by  means  of  a  mechan- 
ical device  which  insures  a  feed  directly  into  the  buckets.  Other 
manufacturers  accomplish  the  same  results  in  different  ways. 

These  conveyors  have  the  widest  range  of  usefulness.  They 
can  be  arranged  to  work  at  any  desired  angle  and  make  any 
desired  turn  in  the  same  vertical  plane.  They  can  transport  ore 
horizontally,  then  vertically,  and  then  horizontally  again,  and 
discharge  anywhere  on  the  line.  They  operate  noiselessly  and 
require  comparatively  little  power  and  very  little  attention. 
Repairs  and  renewals  are  very  low  indeed.  The  capacity  is  large, 
depending  of  course  on  the  size  of  the  buckets  and  their  speed. 
Unfortunately  the  first  cost  is  also  large.  Thus,  a  conveyor  of 
first-class  manufacture,  with  18-  by  24-in.  buckets,  running  at 
10  ft.  per  minute,  which  would  have  a  capacity  for  10  tons  of 
ore  per  hour,  would  cost  about  $3600  for  a  100-ft.  length,  this 
cost  including  the  driving  mechanism  and  electric  motor.  This 
is  much  more  costly  than  any  other  form  of  conveyor  that  has 
been  described  herein.  However,  probably  only  about  1  horse- 
power would  be  required  to  drive  it,  and  repairs  and  renewals 
over  a  considerable  period  of  years  ought  not  to  average  more 
than  1  or  2  per  cent,  per  annum  on  the  first  cost.  Such  low 
figures  are  actually  attained  in  practice.  These  conveyors  are 
therefore  to  be  recommended  for  important  installations  wherein 
belt  conveyors  cannot  be  used,  where  the  first  cost  is  a  minor 
consideration  and  the  assurance  of  certainty  in  operation  is  an 
essential. 


BELT  ELEVATORS 

BY  W.  R.  INGALLS 

(August  15,  1903) 

In  almost  all  ore-milling  operations  one  of  the  most  useful 
and  necessary,  and  at  the  same  time  the  most  objurgated,  pieces 
of  apparatus  is  the  belt  elevator.  Yet  the  belt  elevator,  if  prop- 
erly designed,  should  not  give  any  more  trouble  than  more  com- 
plicated machinery,  which  is  exposed  to  equally  hard  conditions 
of  service.  The  design  and  construction  of  belt  elevators  are 
frequently,  however,  not  what  they  should  be,  and  indeed  author- 
ities differ  materially  as  to  the  nature  of  the  specifications.  Some 
advocate  the  perpendicular  elevator,  others  the  slanting.  Some 
believe  it  to  be  the  best  practice  to  feed  the  ore  directly  into  the 
buckets,  others  arrange  the  feed  so  that  the  buckets  will  scoop 
the  ore  from  the  boot.  Some  use  a  special  boot,  others  do  not. 
There  are  equally  important  differences  of  opinion  as  to  the 
speed  of  the  belt,  spacing  of  the  buckets,  discharge  of  the  ore 
from  the  head  end,  etc. 

The  continuous  band  for  an  elevator  of  this  type  will  be  of 
rubber  belting,  except  in  the  case  of  the  elevator  taking  the  dis- 
charge from  the  drier  in  mills  wherein  the  ore  is  dried,  if  the 
latter  be  so  hot  that  a  rubber  belt  would  be  softened  or  otherwise 
deteriorated;  in  which  case  link  belts  or  chains  passing  over 
sprockets  must  be  used.  In  drying  ore,  in  order  to  insure  good 
screening,  it  has  been  found  to  be  desirable  not  merely  to  drive 
off  the  moisture,  but  also  to  heat  the  ore  to  a  temperature  of 
about  250  deg.  F.,  since  the  hotter  the  ore  the  greater  is  the 
capacity  of  the  screens,  especially  if  the  ore  be  of  a  clayey  nature. 
There  is,  however,  a  limit  to  the  heating  of  the  ore,  which  is  soon 
reached  if  it  is  to  be  handled  directly  from  the  drier  by  means 
of  a  belt  elevator. 

The  belting  for  an  elevator  of  this  type  should  be  of  superior 
quality,  not  less  than  6-ply  in  thickness  for  an  8-in.  or  10-in.  belt. 

185 


186 


METALLURGICAL  MILL  CONSTRUCTION 


Some  authorities  recommend  that  a  10-in.  belt  should  be  of  7-ply; 
a  12-in.  belt  of  9-ply,  a  14-in.  belt  of  9-  to  11-ply,  and  a  16-in. 
belt  of  11-  to  13-ply.  Such  heavy  belts  as  those  last  mentioned 
are  rarely  employed,  and  their  use  is  of  doubtful  advisability  in 
connection  with  the  comparatively  small  head  and  foot  wheels 
that  are  commonly  provided.  However,  it  appears  rational 
enough  to  increase  the  thickness  of  the  belt  as  the  width  increases, 
since  the  capacity  of  the  buckets  and,  consequently,  the  strain 
on  the  belt  increase  at  a  much  greater  ratio.  An  improvement 
over  the  ordinary  belt  is  the  special  elevator  belt,  which  is 
made  by  nearly  all  the  manufacturers  in  this  line,  it  being 
ordinary  belting  surfaced  on  the  outer  side,  or  on  both  sides, 
with  a  covering  of  T^  in.  or  J  in.  of  pure  rubber.  This  covering 
adds  about  12Jc.  per  square  foot  of  surface  to  the  cost  of  the 
belt,  if  TV'm-  thick,  and  twice  as  much  if  J-in.  thick.  This 
makes  a  considerable  increase  in  the  first  cost  of  the  belt,  and 
opinions  differ  as  to  whether  the  increased  wear  justifies  it. 

The  buckets  commonly  employed  are  the  deep  form,  referred 
to  as  "  Style  A,"  made  of  malleable  iron.  These  buckets  are 
seamless,  strong,  and  smooth,  and  their  round  corners  tend  to 
insure  free  delivery  of  the  material  handled.  The  buckets  are 
commonly  spaced  on  the  belt,  from  12  to  20  in.  apart,  center  to 
center.  A  spacing  of  18  in.  is  probably  the  best  practice,  and 
when  a  nearer  spacing  is  employed  it  is  likely  to  be  due  to  the 
attempt  to  obtain  too  large  a  capacity  with  too  small  a  belt. 
The  capacity  of  an  elevator  is  solely  a  function  of  the  volume  of 
the  ore,  the  speed  of  the  belt,  the  spacing  of  the  buckets,  and  the 
size  of  the  buckets.  The  buckets  should  not  be  reckoned  as  run- 
ning more  than  one-third  full.  Assuming  that  the  buckets  are 
running  one-third  full,  are  spaced  18  in.  apart,  and  that  the  belt 
speed  is  300  ft.  per  minute,  the  capacity  of  the  sizes  of  elevator 
most  commonly  used,  in  terms  of  ore  weighing  125  Ib.  per  cubic 
foot,  is  as  follows: 


WIDTH  Or  BELT 

DIMENSIONS  OF 
BUCKETS 

CAPACITY  OF  EACH 

BUCKET 

CAPACITY  OF  ELEVATOR 
IN  TONS  PER  HOUR 

12  in. 
10  in. 
Sin. 

10x6x5     in. 
8x5x4     in. 
6x4x3.5  in. 

160  cu.  in. 
108  cu.  in. 
50  cu.  in. 

22.5 
15.0 
7.0 

CONVEYORS  AND  ELEVATORS  187 

The  head  wheel  should  be  of  sufficient  diameter  to  afford 
proper  friction  for  the  belt.  It  is  seldom  advisable  to  employ  a 
head  wheel  of  less  than  30  in.  diameter,  but  it  is  seldom  necessary 
to  exceed  36  in.  The  diameter  of  the  foot  wheel  is  not  of  so  much 
importance,  but  it  should  not  be  so  small  as  to  cause  thereby  too 
sharp  a  curve  in  the  belt,  depending  upon  the  thickness  of  the  lat- 
ter. A  foot  wheel  20  in.  in  diameter  is  about  as  small  as  ought  ever 
to  be  used,  while  a  30-in.  wheel  is  probably  as  large  as  any  elevator 
will  require.  The  use  of  a  foot  wheel  24  in.  in  diameter  is  a  com- 
mon practice.  The  smaller  the  pulleys  the  more  detrimental  to 
the  belt.  The  belt  should  always  be  2  in.  wider  than  the  buckets. 

The  best  speed  for  a  belt  elevator  is  about  300  ft.  per  minute. 
In  order  to  impart  that  speed,  the  head  wheel  must  run  at  38.2 
revolutions  per  minute  if  30  in.  in  diameter  and  31.8  revolutions 
if  36  in.  in  diameter.  With  a  belt  speed  of  300  ft.  per  minute, 
the  centrifugal  force  throwing  the  ore  out  of  the  buckets  will 
insure  a  satisfactory  discharge,  whether  the  elevator  be  perpen- 
dicular or  sloping. 

As  between  perpendicular  and  sloping  elevators,  the  former 
generally  adapts  itself  the  better  to  the  construction  of  the 
building,  and  permits  in  many  cases  a  simpler  arrangement  of 
the  machinery;  it  is  less  expensive  in  first  cost  and  less  expensive 
to  keep  in  repair  than  the  sloping  elevator.  The  drawback  to  its 
Use  is  the  trouble  in  maintaining  proper  tension  in  the  belt,  as 
the  latter  stretches.  This  must  be  arranged  for  by  the  installa- 
tion of  a  tightener,  which  is  usually  provided  in  the  form  of  an 
adjustable  boot,  wherein  the  foot  wheel  can  be  depressed  as  re- 
quired. If  there  be  insufficient  room  for  lowering  the  boot,  the 
head  of  the  elevator  may  be  so  arranged  as  to  be  raised,  but  the 
latter  expedient  is  seldom  practised,  although  it  is  quite  conven- 
ient in  case  the  driving  belt  from  the  line  shaft  has  a  tightener  on 
it,  or  if  the  line  shaft  and  the  head  of  the  elevator  are  at  the  same 
height  and  not  too  close  together.  In  the  case  of  the  sloping 
elevator,  inclined  at  10  deg.  to  15  deg.  from  the  vertical,  or 
more,  the  belt  is  always  self-tightening,  with  an  elastic  tension, 
the  sag  on  the  descending  side  maintaining  a  sufficient  tension, 
although  the  belt  may  have  stretched  to  a  considerable  extent. 
In  one  case,  a  sloping  elevator,  with  10-  by  6-in.  buckets  and  a 
new  belt,  ran  continuously  for  nine  months  without  any  shortening 
of  the  belt  being  required. 


188  METALLURGICAL  MILL  CONSTRUCTION 

There  is  equally  important  difference  of  opinion  as  to  the  best 
manner  of  feeding  the  ore  into  the  elevator.  Some  mill-men 
advocate  that  the  chute  leading  into  the  boot  should  deliver  the 
ore  16  to  18  in.  above  the  center  line  of  the  foot  wheel.  Others 
recommend  that  it  be  placed  sufficiently  high  so  that  there  will 
always  be  one  or  two  empty  buckets  directly  below  the  one  being 
filled.  Others  prefer  to  allow  the  ore  to  fall  into  the  forward 
slope  of  the  boot  and  be  scooped  up  by  the  buckets  as  they  come 
around.  The  last  method  saves  considerable  hight,  which  is 
important  if  the  foot  of  the  elevator  must  be  placed  in  a  pit,  as 
is  frequently  the  case.  With  a  properly  designed  boot  there  is 
no  danger  of  the  buckets  being  torn  off,  although  the  ore  fed 
may  be  as  coarse  as  2J  in.;  if  by  chance  a  piece  of  ore  wedges 
between  the  edge  of  a  bucket  and  the  boot,  it  is  shoved  upward 
until  the  increased  clearance  allows  the  bucket  to  pass,  when  the 
ore  will  slide  down  again,  and  will  be  taken  up  by  the  next  or 
some  following  bucket.  In  many  elevators  there  is  no  boot 
provided,  the  housing  being  simply  extended  down  to  the  floor 
and  allowed  to  fill  naturally  with  ore,  and  sometimes  there  is  not 
even  any  housing.  An  objection  to  scooping  up  the  ore  is  the 
greater  wear  of  the  buckets,  but  this  is  offset  by  a  greater  wear 
on  the  belt  when  it  is  attempted  to  feed  into  the  elevator  so  that 
the  buckets  will  take  the  ore  "on  the  fly."  In  order  to  avoid  this 
wear  of  the  belt,  some  mill-men  insist  that  the  ore  shall  be  fed 
in  from  the  side,  so  as  not  to  strike  the  belt.  The  usual  practice, 
however,  is  to  feed  directly  toward  the  belt  from  the  front.  At 
the  best,  the  ore  spouted  into  the  elevator  is  seldom  caught  en- 
tirely; there  will  be  some  that  fails  to  be  caught,  which  will  accu- 
mulate in  the  boot  and  will  still  have  to  be  scooped  up. 

An  important  feature  in  the  design  of  a  belt  elevator  is  the 
arrangement  of  the  discharge  end,  in  order  to  insure  a  clean 
delivery  of  the  ore.  Some  mill-men  prescribe  that  the  discharge 
chute  should  take  off  from  the  housing  10  in.  below  the  center 
line  of  the  head  wheel;  others  prescribe  16  in.;  others  measure 
down  27  in.  from  the  center  of  the  head  wheel  shaft  and  then 
draw  a  line  at  an  angle  of  45  deg.,  the  intersection  of  this  line 
with  the  housing  of  the  elevator  being  the  point  at  which  th3 
discharge  chute  takes  off.  The  last  rule  makes  the  elevator 
unnecessarily  high.  It  is  the  practice  of  some  mill-men  to  arrange 
the  discharge  chute  so  that  a  small  quantity  of  ore  will  be  retained 


CONVEYORS  AND  ELEVATORS  189 

at  the  point  where  the  stream  strikes,  in  order  to  protect  the 
bottom  of  the  chute  from  abrasion;  others  arrange  a  special 
casting  of  iron  for  the  ore  to  deliver  upon,  which  is  a  very  good 
device.  There  is  always  likely  to  be  a  small  quantity  of  ore  that 
will  fall  back  into  the  elevator,  and  to  avoid  this  dropping  between 
the  belt  and  the  foot  wheel,  it  has  been  found  a  useful  expedient 
to  insert  a  sloping  partition  at  one  or  two  places  in  the  housing 
of  the  elevator,  inside  of  the  belt,  so  arranged  as  to  discharge  any 
droppings  of  ore  into  a  small  box  outside  of  the  housing. 

In  any  form  of  belt  elevator  it  is  advisable  to  arrange  the 
journals  of  both  the  head  and  the  foot  shaft  so  that  the  bearings 
will  be  as  far  away  from  exposure  to  dust  and  grit  as  possible. 
It  is  still  better  to  arrange  them  so  that  a  stuffing-box  can  be 
inserted  between  the  bearing  and  the  housing  of  the  elevator. 
It  is  one  of  the  bad  features  of  the  adjustable  take-up  boxes 
designed  for  the  boot  by  most  manufacturers  that  the  bearings 
are  arranged  so  closely  to  the  boot  that  it  is  practically  impossible 
to  protect  them  from  grit. 

The  power  required  to  operate  a  belt  elevator  is  comparatively 
insignificant.  The  apparatus  itself  is  in  equilibrium,  and  only 
such  power  has  to  be  applied  as  is  necessary  to  lift  the  ore  and 
overcome  the  friction.  The  theoretical  requirement  of  power  to 
lift  10  tons  per  hour  to  a  hight  of  40  ft.  is  only  0.4  horse-power 
approximately,  and  allowing  an  equal  amount  for  friction,  the 
total  is  only  0.8  horse-power.  If  a  horse-power  costs  $100  per 
annum  (and  in  small  plants  in  the  West  it  is  likely  to  come  to 
about  that  figure),  the  cost  of  running  an  elevator  for  one  year 
for  power  alone  would  be  about  $80.  Assuming  that  this  were 
the  cost  of  operation  for  only  300  days  of  20  hours  each  per 
annum,  the  quantity  of  ore  elevated  would  be  300  X  20  X  10  = 
60,000  tons,  and  the  cost  per  ton  would  be  O.l7c.  Allowing 
0.33c.  per  ton  for  repairs,  which  is  a  liberal  estimate,  the  total 
cost  of  elevation  would  be  only  0.5c.  per  ton.  It  is  evident  that 
there  cannot  be  much  objection  to  the  extensive  use  of  belt 
elevators  on  the  score  of  cost.  The  chief  objection  is  the  loss  of 
time  that  is  likely  to  be  suffered  through  their  breakdown.  This 
can  be  reduced  to  the  minimum  by  the  installation  of  a  well- 
designed  elevator  of  ample  capacity  and  the  best  construction  in 
the  first  place,  and  when  in  operation  by  a  careful  daily  inspection 
and  the  making  of  necessary  repairs  at  convenient  times. 


TAILINGS  ELEVATORS  J 
BY  W.  H.  WOOD  AND  E.  J.  LASCHINGEB 

(March  24,  1904) 

On  the  Witwatersrand,  owing  to  the  flat  nature  of  the  ground, 
it  is  generally  necessary  to  elevate  the  tailings  from  the  mill,  so 
that  the  pulp  may  flow  into  the  vats  of  the  cyanide  annex.  In 
cases  where  the  mill  is  situated  at  a  distance  from  the  cyanide 
works,  it  is  sometimes  even  necessary  to  elevate  the  mill  product 
twice,  in  order  to  obtain  the  requisite  grade  for  the  launders. 
For  this  purpose  tailings  elevators  of  various  kinds  are  employed. 

The  subject  may  be  treated  under  a  few  distinct  headings: 
(1)  Tailings  wheels,  (2)  tailings  pumps,  (3)  bucket  belt  elevators, 
(4)  air-lift  pumps. 

Tailings  Wheels.  —  The  tailings  wheel  is  first  in  importance 
as  being  most  generally  in  use  on  the  Rand;  there  are  quite  a 
number  of  wheels  of  60  ft.  diameter,  capable  of  raising  the  tailings 
from  200  stamps.  Although  the  first  cost  of  a  large  wheel  is 
greater  than  that  of  any  other  elevator,  its  reliability,  durability, 
and  low  maintenance  cost  have  caused  it  to  be  generally  adopted, 
Most  engineers  are  so  conservative  that,  when  once  a  particular 
mechanism  has  proved  itself  satisfactory  to  perform  a  certain 
duty,  they  are  loath  to  experiment  with  others. 

As  to  the  mechanical  efficiency  of  tailings  wheels,  a  test  made 
on  a  25-ft.  wheel  at  the  City  &  Suburban  mine  showed:  Diame- 
ter of  wheel,  25  ft.;  lift  of  wheel,  19  ft.  1  in.;  tailings  and  water 
lifted,  5549  Ib.  per  minute;  theoretical  horse-power,  3.208;  power 
actually  used  to  drive  wheel,  with  two  intermediate  counter-shafts, 
taken  from  motor,  8.847  horse-power;  motor  efficiency  from  actual 
trial,  75  per  cent.;  power  delivered  by  motor,  6.935  horse-power; 
total  power  efficiency  of  wheel  and  driving  mechanism,  48.51  per 
cent. 

1  Abstract  from  the  Journal  of  the  Mechanical  Engineers'  Association  of 
the  Witwatersrand,  Jan.,  1904. 

190 


CONVEYORS  AND  ELEVATORS 


191 


It  must  be  noted  that  as  this  is  a  small  wheel,  and  as  the 
driving  mechanism  involves  three  speed-reductions  from  the 
motor,  the  efficiency  is  probably  much  lower  than  it  would  be  in 
a  large  wheel  driven  from  a  mill  line-shaft  with  only  a  double 
speed-reduction. 

The  usual  type  of  wheel  on  the  Rand  consists  of  an  outer  rim 
with  a  continuous  inner  flange  on  each  side.  The  vanes  are 


FIG.  35.  —  Sand  Wheel. 

straight  and  fixed  to  the  inside  of  the  rim,  between  the  flanges. 
(See  Fig.  35.)  The  outer  rim  is  supported  either  by  rigid  arms  or 
by  tension  spokes,  arranged  in  pairs  and  splayed  out  to  give 
lateral  stiffness.  The  whole  wheel  is  mounted  on  a  heavy  shaft 
and  supported  on  bearings  mounted  either  on  masonry  piers  or 
on  steel  or  wood  structures. 


192 


METALLURGICAL  MILL  CONSTRUCTION 


The  driving  is  accomplished  either  by  belt,  manila  rope,  or 
wire  rope.  It  has  been  found,  after  many  years'  experience,  that 
the  method  of  driving  the  wheels  at  the  Ferreira  Deep,  Henry 
Nourse,  etc.,  has  proved  satisfactory,  that  is,  by  means  of  1.75-in. 
diameter  manila  rope  working  around  grooves  on  the  rope  run  of 
the  wheel,  and  driven  from  11  ft.  diameter  cast-iron,  ordinary 
type,  grooved  driving-wheel. 

A  point  that  is  worth  noting  in  rope-drives  is  that  the  grooves 
in  the  wheels  must  be  at  least  6  in.  deep,  a  precaution  which,  if 
taken,  will  prevent  the  chance  of  the  rope  blowing  off  in  high 

winds.  As  an  actual  proof  of  the  dura- 
bility of  manila  ropes  on  tailings  wheels, 
we  may  mention  that  the  rope  at  the 
Ferreira  Deep  was  put  on  when  the  mill 
first  started,  over  4.5  years  ago,  and 
was  replaced  only  two  months  ago,  and 
that  it  actually  worked  for  3.5  years. 
This  is  a  great  improvement  on  any 
work  done  by  the  older  type  of  belt 
drives,  which,  on  the  average,  we  be- 
lieve, do  not  last  more  than  about 
twelve  months.  Wire-rope  drives  have 

been  tried,  but  so  far  without  success.  The  new  60-ft.  wheel  at 
Knights  Deep  is  driven  this  way,  but  it  has  not  yet  been  working 
long  enough  for  us  to  express  an  opinion. 

Until  recently  the  construction  was  almost  entirely  of  wood, 
but  the  latest  wheels  are  built  of  steel,  all  except  the  lining  of 
the  rim  and  flanges,  and  the  vanes,  which  are  of  wood,  as  being 
the  material  best  adapted  to  resist  the  scouring  action  of  the  sand, 
and  as  being  easily  renewable  in  parts  when  broken  or  worn 
through. 

The  principle  underlying  the  operation  of  these  wheels  is 
exactly  the  reverse  of  the  old-fashioned  overshot  breast  wheel. 
The  liquid  is  introduced  at  the  lowest  point  by  a  launder  delivering 
into  it,  then  raised  up  to  a  point  near  the  top,  where  it  falls  out 
into  a  receiving  launder  as  the  vanes  are  inverted  owing  to  the 
rotation  of  the  wheel,  thus  spilling  the  liquid  out.  (See  Fig.  35.) 

The  calculations  necessary  to  determine  the  carrying  capacity 
of  a  tailings  wheel  are  rather  complicated,  and  it  is  quite  impossible 
to  work  out  exactly  on  theoretical  principles  just  what  maximum 


CONVEYORS  AND  ELEVATORS  193 

amount  of  pulp  a  wheel  can  handle.  This  is  because  it  is  impos- 
sible to  say  how  much  sand  may  remain  permanently  adherent 
to  the  vanes,  and  because  the  surface  of  the  liquid  in  the  buckets 
is  constantly  in  motion.  When  designing  tailings  wheels  for  any 
certain  size  of  mill,  the  following  table  is  useful  in  arriving  at  the 
amount  of  pulp  to  be  handled: 

MILL  PULP  PER  STAMP  PER  MINUTE 


RATIO,  BY  WEIGHT 
WATER  TO  ROCK 

CU.  FT.  OF  PULP 
PER  MINUTE 

LB.  OF  PULP 

PER  MINUTE 

6  —  1 

0.7796 

53.472 

7  —  1 

0.9018 

61.111 

8  —  1 

1.0241 

68.750 

9  —  1 

1.1463 

76.389 

10—1 

1.2685 

84.028 

One  stamp  is  assumed  to  crush  5.5  tons  per  24  hours. 

A  tailings  wheel  has  its  maximum  carrying  capacity  when 
discharging  at  the  level  of  its  axle.  That  is,  if  pulp  is  to  be  lifted 
a  hight  of  20  ft.,  the  wheel  to  lift  a  maximum  quantity  of  material 
will  have  to  be  40  ft.  in  diameter,  but  practical  considerations 
such  as  those  of  cost  and  efficiency  modify  this  deduction  con- 
siderably. The  cost  increases  at  a  greater  rate  than  the  ratio  of 
diameter,  and  it  is  desirable,  especially  for  high  lifts,  to  discharge 
at  a  point  as  high  up  on  the  periphery  as  practicable,  in  order  to 
keep  down  the  size  of  the  wheel.  To  meet  this  requirement  the 
angle  made  by  the  vanes  with  the  tangent  to  the  periphery  must 
be  so  chosen  that  the  vane  makes  a  small  angle  with  the  hori- 
zontal at  the  point  of  commencement  of  discharge.  This  is  done 
by  making  a  judicious  selection  in  determining  the  diameter  of 
the  tangent  circle  of  vanes. 

The  time  to  be  allowed  for  the  buckets  to  discharge  their 
contents  should  not  be  less  than  3  sec.  for  wheels,  say,  of  40  ft. 
diameter,  and  about  5  sec.  for  wheels  of  60  ft.  diameter;  that  is, 
the  receiving  platform  should  be  long  enough,  or  the  speed  of 
the  wheel  slow  enough,  that  the  buckets  will  take  the  stipulated 
time  to  travel  over  the  receiving  platform  when  they  are  in  their 
inverted  position  in  the  upper  portion  of  the  wheel. 

From  theoretical  considerations  it  is  evident  that,  the  larger  a 
wheel,  the  greater  the  ratio  of  lift  to  diameter  may  be,  and  also 
that  larger  wheels  may  be  run  at  a  higher  peripheral  velocity 


194 


METALLURGICAL  MILL  CONSTRUCTION 


than  small  ones.  It  is  evident  also  that  a  wheel  could  be  revolved 
at  such  a  rate  that  it  would  not  discharge  at  all,  but  carry  its 
contents  completely  round  and  round,  owing  to  the  centrifugal 
force  becoming  greater  than  the  weight  of  the  liquid. 

The  following  table  of  " critical"  or  limiting  speeds  for  wheels 
of  various  diameters  will  be  of  service: 


DIAM.  OF  WHEEL 
IN  FT. 

REV.  PER  MINUTE 

PERIPHERAL  VEL. 
FT.  PER  MINUTE 

10 

24.218 

761 

20 

17.125 

1,076 

30 

13.983 

1,318 

40 

12.110 

1,522 

50 

10.830 

1,701 

60 

9.887 

1,863 

70 

9.154 

2,013 

80 

8.562 

2,152 

The  actual  speed  in  practice  is,  of  course,  considerably  less 
(generally  about  one-third  of  the  critical  speed,  as  given  in  the 
above  table),  but  it  is  advisable  to  run  at  as  high  a  rate  as  possible, 
in  order  to  keep  down  the  weight  and  cost  of  the  wheel. 

From  a  consideration  of  the  strain  diagrams  for  tailings  wheels, 
it  appears  that  the  strain  on  the  rim  is  independent  of  the  number 
of  spokes,  and  this  is  true  within  the  limits  of  practice;  it  is  also 
evident  that  the  wheel  with  rigid  arms  is  to  be  preferred  to  the 
wheel  with  tension  spokes,  because  the  maximum  strains  are  only 
about  half  as  great  in  the  rigid  armed  wheel  as  in  the  spoke 
wheel.  Practical  considerations  also  point  to  the  advisability  of 
making  the  wheel  with  rigid  arms,  as  it  is  easier  to  make  it  run 
true.  The  tension  spoke  wheel  looks  lighter  and  prettier,  and 
may,  perhaps,  be  slightly  cheaper;  but  for  durability  and  rigidity 
the  heavy  armed  wheel  is  superior  and  more  satisfactory. 

The  rim  of  a  tailings  wheel  is  generally  the  weak  part  in  its 
design  and  construction,  and,  owing  to  the  heavy  and  varying 
strain,  it  is  more  likely  to  give  trouble  than  any  other  part  of  the 
wheel.  It  has  been  suggested  by  L.  H.  Lavenstein  to  make  the 
vanes  of  a  V  shape,  with  the  object  of  obtaining  a  cleaner  discharge 
of  the  heavy  sands  which  stick  to  the  buckets.  Mr.  Lavenstein 
has  also  designed  a  spokeless  wheel  which  consists  simply  of  a 
stiff  rim,  with  the  usual  buckets,  guided  by  rollers,  and  driven  by 
the  friction  of  driving-wheels  set  under  the  rim  of  the  tailings 


CONVEYORS  AND  ELEVATORS  195 

wheel,  which  has  continuous  railway  rails  around  its  outer  pe- 
riphery. The  object  of  this  invention  is  to  simplify  the  driving 
gear  with  its  usual  great  speed  reduction,  and  to  save  the  cost  of 
the  heavy  foundations  or  framework  required  to  support  the 
bearings  of  the  ordinary  wheel.  The  rim  of  such  a  wheel  would , 
of  course,  have  to  be  very  strong  and  stiff  to  resist  deformation 
if  the  wheel  were  of  large  size.  We  do  not  know  of  this  type  of 
wheel  having  been  actually  constructed  and  put  into  operation. 

(2)  Tailings  Pumps.  —  Plunger  pumps  are  used  on  some 
mines  to  elevate  the  mill  pulp.  They  are  usually  made  of  the 
single-acting  type,  with  long  stroke  and  comparatively  low 
plunger  speed.  The  plungers  must  have  clean  water  delivered 
under  pressure  behind  the  gland  packing  to  wash  off  the  sharp 
sand  from  the  plunger  on  its  return  stroke  and  thus  prevent  the 
rapid  grinding  away  of  the  plunger  and  gland.  The  greatest 
difficulty  encountered  is  that  of  the  scouring  of  the  valve  ports 
and  valve  chambers  by  the  sands  carried  in  the  water.  This  is 
minimized,  in  pumps  of  good  design,  by  making  the  ports  as  large 
as  possible,  thus  keeping  down  the  velocity  of  the  pulp  when 
passing  through  them.  A  certain  minimum  velocity  of  flow, 
however,  must  be  kept  up  in  order  to  prevent  the  settling  of  the 
pyrite  and  heavier  sands.  Removable  liners  in  parts  subject  to 
scour  are  also  provided. 

A  well-designed  tailings  pump  is  expensive,  because  of  its 
size;  it  is  required  to  handle  so  large  a  quantity  of  liquid  that  all 
the  parts  are  necessarily  massive.  The  chief  drawback,  however, 
is  the  maintenance  cost,  and,  more  particularly,  the  loss  due  to 
mill  stoppage  when  repairs  have  to  be  made.  The  smallest  item 
is  generally  the  power  cost;  maintenance  costs  come  next  in 
importance,  and  the  greatest  loss  is  the  reduction  in  gold  recovery, 
due  to  stoppages  of  the  mill. 

While  upon  this  subject  it  is  well  to  point  out  how  important 
it  is  that  every  plant  should  be  provided  with  either  a  duplicate 
set  of  tailings  elevators  or  some  other  alternative  method  of 
raising  the  pulp  while  the  elevator  usually  in  use  is  shut  down 
for  repairs.  It  might  easily  happen  that  the  loss  due  to  a  single 
breakdown  in  a  tailings  elevator  would  more  than  pay  for  the 
installation  of  the  most  expensive  kind  of  elevator  known,  as  an 
alternative  for  doing  this  work  in  case  of  accident. 

Centrifugal  pumps  have  been  tried,  but  those  who  have  had 


196  METALLURGICAL  MILL  CONSTRUCTION 

experience  are  best  able  to  testify  to  the  uselessness  of  the  cen- 
trifugal pump  for  this  class  of  work.  The  vanes  may  be  scoured 
away  by  the  sand  in  a  few  hours,  leaving  nothing  but  the  hub 
remaining  on  the  shaft.1 

Plunger  pumps  and  centrifugal  pumps  may  be,  and  are, 
successfully  used  for  elevating  slimes,  but  when  handling  mill 
pulp  the  sharp  grains  of  quartz  cause  so  much  scouring,  neces- 
sitating so  many  and  frequent  repairs,  as  to  render  them  but 
poor  substitutes  for  tailings  wheels. 

(3)  Bucket  Belt  Elevators.  —  Buckets  fixed  either  to  link  chain 
or  to  rubber  belts  have  been  tried  for  elevating  tailings.     Owing 
to  the  sharp  sand  particles  lodging  in  the  moving  parts  or  joints 
of  a  link  chain,  the  links  are  soon  cut  through.     In  the  case  of 
buckets  fixed  to  a  rubber  or  composition  belt  the  chief  difficulty 
that  seems  to  present  itself  is  that  of  driving.     The  belt,  being 
continually  wet,  slips  on  the  pulleys,  and  if  sufficient  tension  is 
employed  to  make  the  belt  grip,  the  strain  is  too  great  and  the 
belt  tears  apart.1 

(4)  Air-lift  Pumps.  —  The  air-lift  or  Pohle  pump  has  recently 
come  in  for  a  great  deal  of  discussion  as  to  its  adaptability,  du- 
rability, and  efficiency  as  a  tailings  elevator.     That  it  can  be 
successfully  employed  for  this  work  has  been  demonstrated  in 
actual  practice.     It  is  used  in  Australia  in  a  number  of  mines 
for  raising  pulp  to  a  small  hight. 

What  its  life  may  be  is  not  so  well  known.  The  fluid  must 
be  kept  moving  at  a  rather  rapid  rate  in  this  style  of  elevator, 
and  the  scouring  action  of  the  sands  on  the  metallic  pipes  may 
be  so  considerable  as  to  require  frequent  renewals  of  the  piping. 
It  would  appear  that  thick  cast-iron  pipes  would  be  best  to  use, 
or  very  cheap  and  durable  piping  might  be  made  of  wood,  which 
has  remarkable  wearing  qualities  where  scouring  action  is  con- 
cerned. There  are  no  valves  or  moving  parts  to  give  trouble, 
and  at  first  glance  this  apparatus  appears  to  present  many 
commendable  features. 

.  The  mechanical  efficiency  of  this  device  is  somewhat  disap- 
pointing. Sufficient  reliable  tests  have  not,  so  far  as  we  are  aware, 
been  made  or  published  to  enable  one  to  predict  with  certainty 
what  efficiency  may  be  expected  from  any  particular  pump 

1  Both  centrifugal  pumps  and  bucket  belts  are  extensively  used  for  the 
elevation  of  tailings  and  other  mill  products  in  the  United  States.  —  EDITOR. 


CONVEYORS  AND  ELEVATORS  197 

operating  on  this  principle.  Some  tests  on  the  Pohle  pump  for 
lifting  water  have  been  published.1  From  these  records  it  appears 
that  the  efficiency  is  not  high  (about  one-half  that  of  a  pump), 
and  varies  with  a  good  many  factors,  such  as  ratio  of  submersion 
to  lift,  size  of  air  pipe,  hight  of  lift,  etc. 

The  whole  question  of  tailings-elevator  arrangements  may  be 
summarized  thus:  Install  the  most  efficient,  durable,  and  reliable 
elevator  to  do  the  regular  work,  even  if  the  first  cost  be  high. 
Install  a  stand-by  which  is,  first  of  all,  reliable,  but  as  simple  and 
cheap  as  possible;  whether  it  is  efficient  or  inefficient  is  practically 
immaterial. 

We  wish,  however,  to  point  out  that  if  a  really  well-designed 
tailings  wheel  is  installed,  it  is  doubtful  whether  there  is  any 
necessity  to  have  a  stand-by  apparatus,  as  the  satisfactory  record 
of  the  tailings  wheel  at  the  Ferreira  Deep  illustrates.  But  if  in 
a  large  plant  two  or  more  tailings  wheels  are  required,  and  they 
are  not  far  distant  from  each  other,  it  will  be  advisable  to  install 
a  cheap  stand-by,  as  the  risk  of  breakdown  increases  in  direct 
proportion  to  the  number  of  elevators  required.  The  stand-by 
should  then  be  so  arranged  as  to  do  the  work  of  either  or  any 
one  of  the  tailings  wheels. 

1  "Mine  Drainage,  Pumps,  etc./'  H.  C.  Behr,  p.  170,  Engineering,  Aug.  17, 
1900;  and  paper  by  William  Maxwell,  British  Association  of  Waterworks  En- 
gineers, The  Engineer,  Aug.  14,  1903. 


TAILINGS  ELEVATORS 

BY  R.  OILMAN  BROWN 

(April  14,  1904) 

Apropos  of  the  interesting  paper  by  Messrs.  W.  H.  Wood  and 
E.  J.  Laschinger,  published  in  abstract  in  the  Engineering  and 
Mining  Journal  of  March  24,  the  following  notes  concerning 
different  devices  for  lifting  stamp-mill  tailings  may  be  of  general 
interest.  They  are  the  result  of  experiences  in  the  20-stamp  mill 
of  the  Standard  Consolidated  Mining  Company,  at  Bodie,  Cali- 
fornia: 

Air-lift.  —  The  problem  was  to  raise  60  tons  of  the  quartz 
sand  and  about  90,000  gallons  of  water  per  day  45  ft.  This  was 
equivalent  to  about  9.4  cu.  ft.  per  minute,  weighing  604  Ib.  The 
theoretical  horse-power  in  consequence  was  less  than  0.85.  The 
efficiency  of  an  air-lift  is  dependent  upon  the  ratio  of  submersion 
to  lift,  and  accordingly  a  double  lift  was  determined  upon,  to 
avoid  expense  in  obtaining  submersion.  A  shaft  was  sunk  under 
the  mill  and  a  10-in.  pipe  placed  in  it,  closed  at  the  bottom. 
Within  this  a  3-in.  lift-pipe  was  placed.  This  pipe  gave  a  lift  of 
22.5  ft.  above  the  top  of  the  10-in.  pipe,  and  discharged  into 
another  10-in.  submersion  pipe,  with  3-in.  lift  as  before,  giving 
22.5  ft.  of  additional  lift.  The  air  supply  was  from  a  Garden 
City  rotary  blower,  capable  of  displacing  188  cu.  ft.  of  free  air 
per  minute  and  delivering  it  at  10  Ib.  pressure.  The  air-pipe 
was  1  in.  and  came  down  outside  the  lift-pipe,  turning  up  a  few 
inches  within  the  lower  end.  This  device  operated  with  fair 
success,  but  when  part  of  the  mill  was  idle,  the  lowered  velocity 
in  the  lift-pipe  allowed  the  heavier  particles  to  settle  against 
the  rising  current  and  in  time  blocked  the  pipe.  No  tests  for 
power  consumption  were  made,  but  the  efficiency  would  be  at 
best  poor.  I  have  recently  been  using  an  air-lift  for  unwatering 
a  mine  under  conditions  where  pumping  was  impossible,  and  have 
found  everything  satisfactory  in  its  use,  except  the  efficiency. 

198 


CONVEYORS  AND  ELEVATORS  199 

This  was  about  12  per  cent,  measured  between  the  electric  meters, 
measuring  the  current  which  operated  the  air-compressor  and 
the  actual  water  thrown.  The  air  pressure  was,  however,  85  lb.; 
in  the  case  of  the  Garden  City  blower,  giving  but  10  lb.  pressure, 
the  efficiency  would  be  better.  It  should  be  added  that  this 
efficiency  was  for  the  case  of  the  submersion  being  equal  to  lift. 

Bucket  Elevator.  —  This  was  also  tried,  but  so  much  sand 
adhered  to  the  buckets  that,  apart  from  the  wear  on  the  links, 
the  system  was  not  satisfactory,  particularly  during  cold  weather. 

Centrifugal  Pump.  —  This  was  used  for  a  year  or  so  for  this 
service,  notwithstanding  the  heavy  wear.  The  consumption  of 
metal  from  this  cause  was  lessened  by  various  expedients,  but 
probably  at  best  it  amounted  to  4c.  or  5c.  per  ton  of  sand  handled. 
Added  to  this  was  the  high  power  consumption.  The  mill  was 
operated  by  electricity,  and  meter  measurements  made  at  the 
main  motor  showed  15.5  horse-power  as  the  consumption  of  the 
centrifugal  pump,  including  belting,  line-shaft  running,  etc.  This 
may  be  considered  by  far  the  most  serious  drawback  to  the  cen- 
trifugal pump  for  this  work.  I  believe  that  the  consumption  of 
metal  can  be  still  further  lessened  by  changes  in  design. 

Frenier  Pump.  —  This  somewhat  anomalous  machine  has  been 
doing  excellent  service  and  has  shown  no  excessive  wear,  the 
chief  wearing  part  being  the  stuffing-box  in  the  axis.  The  power 
consumption  is  less  than  one-third  that  of  the  centrifugal  pump. 
The  speed  must  be  closely  adjusted  to  get  good  results,  and  the 
pump  is  sensitive  to  sudden  increase  or  decrease  of  flow  delivered 
to  it,  change  in  either  direction  causing  the  supply-box  to  over- 
flow until  the  pump  has  adjusted  itself  to  the  changed  condition. 
For  ordinary  work  in  small  units  it  is  by  long  odds  the  best  of  the 
machines  enumerated  above.  As  45  ft.  is  an  excessive  lift  for 
these  pumps,  we  used  two  54-in.  pumps,  one  lifting  to  the  other. 


PART  VI 
DISPOSAL  OF  TAILINGS 


A  SYSTEM  OF  HANDLING  SAND  MECHANICALLY 
FOR  CYANIDE  VATS l 

BY  CHARLES  BUTTERS  AND  ALBERT  F.  CRANK 

(December  5,  1903) 

The  Virginia  City  works  of  Chas.  Butters  &  Co.,  Ltd.,  are 
situated  on  the  eastern  side  of  a  canon  leading  down  from  Virginia 
City,  and  at  a  point  about  three  miles  distant  from  that  town. 
This  site  was  chosen,  close  to  a  large  heap  of  tailings,  in  order  to 
conveniently  treat  not  only  these  tailings,  but  also  ore  from  the 
Comstock  lode  and  other  veins  in  the  vicinity.  An  inclined 
tramway  with  two  lines,  worked  by  a  wire  rope,  is  carried  west- 
ward from  the  works  across  the  canon  by  a  wooden  trestle  bridge, 
and  continued  for  1200  ft.  along  the  length  of  the  heap.  The 
tailings  are  loaded  by  horse  scrapers  direct  into  the  tram-cars, 
for  transport  to  the  works. 

As  there  is  a  fall  of  600  ft.  between  the  mean  level  of  Virginia 
City  and  the  works,  tailings  can  be  sluiced  down  by  a  small  stream 
of  water  from  any  heap  in  the  camp,  along  a  lOxlO-in.  wooden 
flume,  direct  to  the  classifier  in  the  works.  About  three  miles 
of  main  flume  and  a  mile  of  branch  flume  have  been  built,  and 
are  now  in  successful  operation. 

The  tramway  and  flume  enable  tailings  to  be  conveyed  to  the 
works  at  an  exceedingly  low  cost  per  ton,  as  the  amount  of  shov- 
eling is  reduced  to  a  minimum.  The  next  point  is  to  be  able  to 
handle  the  sand  economically  between  the  collecting  and  leaching 
vats,  and  discharge  it  to  the  waste  heap. 

The  works  are  designed  principally  for  the  treatment  of  slimes, 
which  make  up  55  per  cent,  of  the  total  amount  of  material 
treated,  the  remaining  45  per  cent,  being  sand.  Consequently, 
as  275  tons  are  treated  daily,  124  tons  of  sand  have  to  be  dealt 
with.  Labor  in  this  district  is  scarce,  and  workmen  command 

1  Abstract  of  a  paper  read  before  the  Institution  of  Mining  and  Metallurgy, 
London,  Nov.  19,  1903. 

203 


204  METALLURGICAL  MILL  CONSTRUCTION 

high  wages;  therefore,  supposing  hand  work  to  be  adopted,  the 
capacity  of  the  sand  department  would  be  governed  by  the 
amount  of  labor  available  for  shoveling,  while  the  value  of 
the  tailings  that  could  be  worked  at  a  profit  would  in  part  depend 
upon  the  expense  of  this  labor. 

The  machines  adopted  to  do  the  work  are  portable  excavating 
and  distributing  appliances,  capable  of  dealing  with  damp  or 
drained  sand.  They  are  the  invention  of  Hiram  W.  Blaisdell, 
of  Los  Angeles,  Cal.  It  was  claimed  that  they  would  discharge, 
transfer,  and  distribute  more  sand  in  a  given  time  than  was 
possible  by  hand  labor,  even  when  mechanical  conveyors  were 
employed.  It  was  further  said  that  all  the  labor  in  the  sand-house 
could  be  done,  according  to  the  size  of  the  works,  by  one  or  two 
attendants.  Lastly,  it  was  claimed  that,  owing  to  the  thorough 
mixing  during  the  process  of  excavation,  and  to  the  subsequent 
light  and  even  distributing  of  the  material  in  the  vats,  the  cyanide 
solution  penetrated  more  rapidly  and  leached  more  completely 
than  in  any  light  system  now  in  vogue.  As  the  Blaisdell  ma- 
chines are  new  factors  in  cyanide  practice,  it  is  well  to  describe 
them  fully,  and  to  state  the  results  obtained,  as  the  matter  is 
sure  to  be  of  interest  to  mining  engineers  engaged  in  similar 
operations. 

From  August  4  to  August  7  of  this  year  a  series  of  records 
were  taken  of  daily  performance  under  regular  working  conditions. 
The  results  obtained,  together  with  the  records  of  the  past  six 
months,  confirm  the  original  estimate  of  the  value  of  the  system, 
and  substantiate  the  claims  advanced  by  the  manufacturers. 
At  the  present  time,  the  amount  of  material  treated  daily  in  this 
department  is  250  tons — that  is  to  say,  125  tons  are  handled  twice 
in  that  period.  Under  the  direction  of  the  manager  of  the  works, 
the  shiftsman  on  the  sand  tanks  makes  the  required  changes  in 
pump  connections,  valves,  and  solutions,  and  operates  the  exca- 
vating plant  in  a  working  day  of  10  hours. 

The  accompanying  plan  exhibits  the  general  arrangement  of 
this  sand-handling  plant.  It  consists  of  a  Butters  distributor, 
for  charging  the  collecting  vats;  one  Blaisdell  bottom-discharge 
excavator,  for  discharging  all  the  vats;  one  Blaisdell  centrifugal 
distributor,  for  charging  the  vats;  and  a  combination  of  four 
16-in.  belt  conveyors,  for  transport  of  the  sand, 

There  are  eight  wooden  tanks,  or  vats,  each  30  ft.  diameter 


DISPOSAL  OF  TAILINGS 


205 


MJLttOM 


206  METALLURGICAL  MILL  CONSTRUCTION 

by  6  ft.  deep,  intended  for  125  tons  of  sand  each;  they  are  set 
upon  one  continuous  foundation.  Each  vat  has  a  central  dis- 
charge gate,  with  chute  leading  to  a  conveying  belt  below.  The 
two  north  vats  are  used  for  collecting  and  draining  the  sands 
received  from  the  tailings  wheel,  and  their  contents  are  subse- 
quently removed  to  one  of  the  six  leaching  vats  for  cyanide 
treatment. 

Conveyor  No.  1,  located  below  the  two  collecting  vats,  is 
approximately  65  ft.  long,  and  conveys  to  the  left,  or  northward. 
Conveyor  No.  2  is  20  ft.  long,  and  conveys  the  discharge  of  No.  1 
at  right  angles,  delivering  to  conveyor  No.  3,  also  at  right  angles. 
At  the  north  end,  where  the  discharge  of  No.  2  is  received,  con- 
veyor No.  3  has  an  inclination  of  about  11  deg.  for  67  ft.,  beyond 
which  it  runs  level  for  123  ft.  to  the  end  of  the  line  of  vats.  By 
this  incline  the  sand  is  brought  from  a  level  4  ft.  below  the  bottom 
of  the  vats  to  a  level  18  in.  above  their  tops.  In  ground  plan 
this  conveyor  is  parallel  with  the  line  of  vats,  with  a  distance  of 
17  ft.  8  in.  between  center  lines.  A  tripper  extends  from  the 
Blaisdell  distributor  and  diverts  the  load  from  conveyor  No.  3 
to  a  short  conveyor  upon  the  machine.  Conveyor  No.  4  is 
placed  below  the  discharge  gates  of  the  six  leaching  vats,  and  is 
arranged  so  that  it  can  be  run  in  either  direction.  When  running 
north  (or  to  the  left),  the  discharge  from  leaching  vats  is  delivered 
upon  conveyor  No.  1,  and  then  carried  around  the  system  to  the 
distributor.  When  running  south,  the  discharged  tailings  are 
carried  to  the  waste  heap.  In  place  of  No.  4  conveyor,  a  launder 
leading  to  the  waste  pump  is  employed  when  single-treatment 
sand  is  being  worked. 

The  excavating  and  distributing  machines  are  movable  steel 
structures,  spanning  the  tanks  and  traveling  upon  16-lb.  rails 
placed  9  in.  outside,  12  in.  above,  and  extending  the  length  of 
the  line  of  vats.  It  has  been  found,  with  the  use  of  this  system, 
that  the  pulp  is  laid  down  so  perfectly  in  the  vats  that  no  bene- 
fits were  derived  by  the  use  of  a  second  treatment;  and,  al- 
though the  plant  was  laid  out  for  giving  a  second  treatment, 
or  several  treatments,  to  any  vat,  these  have  been  found  un- 
necessary and  have  been  discontinued. 

As  employed  in  these  works,  the  Blaisdell  excavator  consists 
of  a  steel  truss  bridge,  supporting  at  midspan  the  excavator 
and  driving  gears,  and  at  one  end  the  motor  and  traverse  gears. 


DISPOSAL  OF  TAILINGS  207 

The  bridge  deck  is  33  ft.  over  all  in  length  and  5  ft.  6  in.  wide. 
The  hight  of  the  truss  is  10  ft.  The  bridge  is  supported  upon 
trucks,  each  of  which  contains  two  15-in.  flanged  wheels,  10  ft. 
between  centers.  The  span  or  distance  between  rail  centers  is 
31  ft.  6  in.  The  midspan  vertical  truss  bridge  carries  cross-head 
guides,  together  with  the  heavy  screws  for  raising  and  lowering 
the  cross-head.  The  latter  contains  the  upper  bearing  of  the 
spindle,  and  a  thrust-box  supporting  the  weight  of  the  spindle, 
excavator  beam  and  disks.  A  heavy  frame  in  the  bridge  floor 
carries  a  bearing,  in  which  rests  the  main  bevel  gear-wheel, 
driving  the  excavator  spindle.  This  gear  serves  also  as  the 
lower  guide  for  the  spindle,  and  is  centered  below  the  cross-head 
bearing.  Power  is  transmitted  to  the  spindle  by  steel  keys 
secured  in  the  gear,  and  entering  keyways  cut  the  full  operating 
length  of  the  spindle.  Securely  keyed  to  the  lower  end  of  the 
latter  is  a  cruciform  beam  of  structural  steel  parts. 

The  total  over-all  length  of  the  two  long  arms  is  29  ft.  8  in., 
thus  allowing  a  2-in.  clearance  when  operating  a  30-ft.  vat. 
The  short  arms  have  an  over-all  length  of  11  ft.  4  in.  Bolted  to 
the  under  side  of  these  arms  are  cast-iron  hangers  of  graduated 
lengths,  each  terminating  in  a  bearing,  wherein  revolve  hardened 
steel  spindles  projecting  from  the  center  of  the  steel  excavator 
disks.  These  bearings  are  so  designed  that  sand  may  not  enter. 

The  disks  are  placed  obliquely  to  the  radial  lines.  The  angle 
varies  from  15  to  25  deg.,  the  large  angle  bearing  nearest  the 
center.  Twelve  disks  about  the  center  are  flat  plates,  while  all 
other  disks  are  dished  with  spindles  projecting  from  their  side. 
The  concave  side  is  presented  to  the  work.  There  are  in  all 
46  disks,  so  spaced  from  the  center  that  the  position  of  each 
disk  upon  its  respective  arms  falls  upon  a  spiral  generated  from 
the  center,  in  the  direction  of  rotation  of  the  beam.  A  radial 
section  of  the  contents  of  a  vat  during  excavation  would  show  a 
series  of  36  surface  undulations.  The  hollow  of  these  waves  will 
rest  upon  a  line  having  a  fall  toward  the  center  of  about  1  in. 
in  12  ft. 

The  angular  setting  upon  the  arms  presents  the  edge  of  the 
disks  to  the  work  as  a  cutting  line.  As  this  advances,  the  sand 
is  cut  with  a  rolling  and  nearly  vertical  motion,  with  little  friction. 
The  line  of  cut  extends  in  a  diagonal  across  the  furrow,  and  a 
shearing  rather  than  scraping  action  is  secured.  The  dished 


208  METALLURGICAL  MILL  CONSTRUCTION 

shape  of  the  outer  disks  gives  the  necessary  lead  and  clearance 
to  the  cutting  edge.  As  the  disks  revolve  only  when  in  contact 
with  the  sand,  it  follows  that  there  is  no  friction  due  to  drag, 
so  that  the  power  over  and  above  that  required  to  overcome 
internal  machine  frictions  and  the  insertion  of  the  cutting  edges 
is  applied  to  the  actual  moving  of  sand.  This  is  raised  by  the 
revolving  disks  until  dislodged  by  gravity,  when  it  rolls  from  the 
dished  surface  into  the  path  of  the  following  disk.  The  weight 
of  the  beam,  with  spindle  and  disks,  is  sufficient  to  force  the  disks 
into  the  sand,  but  the  depth  of  cut  is  regulated  by  the  feed- 
screws. These  receive  automatic  motion,  or  feed  from  the  bevel 
gear  pinion-shaft  by  means  of  a  pawl,  ratchet-wheel,  and  a 
gear-chain.  The  pawl  makes  25  strokes  per  minute,  and  may  be 
set  as  desired  to  feed  from  one  to  seven  teeth  upon  the  ratchet- 
wheel  with  a  beam  revolution  of  five  per  minute.  This  produces 
a  vertical  motion  of  the  excavator  spindle  of  from  0.02  to  0.135  in. 
per  revolution.  The  range  of  adjustment  allows  the  work  of 
excavation  to  be  pushed  to  the  maximum  limit  permitted  by  the 
firmness  of  the  sand  or  the  capacity  of  the  conveyors.  There  is, 
in  addition,  a  belted  connection  between  the  ratchet-wheel  shaft 
and  the  main  shaft,  by  which  a  vertical  speed  of  14  in.  per  minute 
may  be  secured  for  rapid  raising  after  excavating  or  for  adjust- 
ment before  a  run. 

An  automatic  device  upon  the  cross-head  guide  may  be  set 
to  stop  the  excavator  at  any  desired  depth,  and  a  similar  device 
in  a  permanent  position  at  the  top  of  the  guides  prevents  injury 
from  raising  the  beam  too  close  to  the  bridge. 

Power  for  the  machine  is  taken  from  two  overhead  wires  by 
a  trolley,  and  supplied  to  a  direct-connected  motor  upon  the 
bridge,  where  is  also  located  the  switchboard  panel,  containing 
the  rheostat  with  reversing  switches  and  fuse-block.  The  motor 
is  back-geared  to  a  line  of  shafting  extending  to  the  center  of  the 
bridge.  From  this  shaft,  power  is  taken  to  operate  the  traverse 
gear  train  for  the  following  four  purposes:  Shifting  from  vat  to 
vat,  operating  the  boring  bar,  rapidly  raising  and  lowering  the 
feed,  and  driving  the  counter-shaft  of  the  excavator  spindle  gears. 

In  dealing  with  a  filled  vat,  the  boring  head  is  first  brought 
over  the  opened  central  discharge  valve  and  driven  through  the 
sand.  The  excavator  beam  is  then  raised  to  clearance  position, 
and  is  brought  over  the  discharge  opening  by  moving  the  bridge 


DISPOSAL  OF  TAILINGS  209 

forward.  The  beam  is  now  lowered  until  the  disks  meet  the  sand, 
when  the  revolving  gears  may  be  started  and  the  required  feed 
set.  The  machine  then  runs  without  attention  until  it  comes 
into  contact  with  the  automatic  stop. 

The  Blaisdell  centrifugal  distributor  is  supported  at  midspan 
of  a  movable  steel  bridge  having  a  deck  and  trucks  similar  in 
design  to  those  of  the  excavator.  It  is  not  as  heavy  in  construc- 
tion, and  the  trussing  is  secured  by  suspension  rods  and  spreader 
below  the  deck.  At  one  end  of  this  bridge  a  tripper  is  placed, 
overhanging  conveyor  No.  3,  and  diverting  the  sand  from  the 
latter  to  a  conveyor  upon  the  bridge  deck.  This  discharges  into 
a  cast-iron  hopper  at  the  bridge  center.  A  revolving  vertical 
spindle  passes  through  the  hopper  and  has  a  horizontal  steel 
disk  keyed  upon  the  lower  end.  Riveted  to  the  upper  surface 
of  this  disk  are  short  radial  vanes  of  angle  iron.  This  distributor 
and  spindle  are  supported  by  bearings  above  the  hopper.  Pedes- 
tals extend  upward  from  the  hopper,  and  contain  the  bearings 
mentioned  and  those  of  the  bevel-gear  shafts.  The  pinion-shaft 
of  the  latter  is  belted  to  the  head  shaft  of  the  bridge  conveyor. 

The  vaned  disk,  or  distributor,  revolves  rapidly,  and  sand 
falling  from  the  hopper  upon  the  whirling  surface  is  showered 
evenly  over  the  vat  surface  below.  Power  for  the  distributor  is 
taken  from  the  overhead  wires  in  similar  manner  as  for  the  exca- 
vator. The  speed  of  revolution  may  be  changed  by  both  cone 
pulleys  or  rheostat. 

A  cylindrical  guard-ring  of  light  sheet-iron,  15  in.  wide  and 
24  ft.  in  diameter,  surrounds  the  distributor.  It  is  supported 
upon  brackets  extending  from  the  bridge,  and  has  a  3-in.  clearance 
over  the  side  of  the  vats.  This  ring  prevents  the  loss  of  stray 
sand  particles  when  filling  near  the  top  of  the  vat.  When  working 
the  distributor,  the  shiftsman  starts  the  traverse  gears,  and  runs 
the  distributor  into  position  over  the  closed  central  valve  of  an 
empty  leaching  vat.  He  then  starts  the  distributor  and  con- 
veyor. Leaving  the  machine,  he  passes  along  the  sand-house 
to  the  switchboard  of  the  motor  driving  the  conveyors.  After 
starting  the  conveyors,  he  passes  on  to  the  excavator,  which  he 
has  previously  placed  in  position.  He  now  starts  it,  and  after 
watching  for  a  few  minutes,  to  see  that  the  feed  of  excavation  is 
properly  set,  he  leaves  it  to  itself. 

This  machinery,  during  the  present  year,  has  demonstrated 


210  METALLURGICAL  MILL  CONSTRUCTION 

that  the  work  in  the  sand-house  may  be  executed  regularly  in  a 
given  time  entirely  independent  of  labor  conditions.  Both  the 
supply  and  cost  of  labor  may  be  disregarded,  for  the  primary 
consideration  has  now  become  merely  the  cost  of  power.  It  has 
been  demonstrated  that  the  cost  per  ton  for  handling  a  given 
quantity  of  sand  between  the  tailing  wheel  and  waste  dump, 
once  or  oftener,  may  be  determined  in  advance  to  a  nicety.  The 
tests  show  that  the  cyanide  manager  has  in  the  excavator  a 
valuable  instrument,  which  is  of  service  also  in  understanding 
correctly  the  conditions  existing  in  the  leaching  and  collecting 
vats.  The  power  required  to  discharge  a  vat  may  be  quickly 
determined  by  the  readings  from  the  volt  and  ammeter.  Com- 
parison between  this  reading  and  a  standard  table  of  reading 
will  show  the  degree  of  firmness  with  which  the  sand  is  packed 
in  the  vat. 

An  uncalled-for  rise  in  the  power  used  under  regular  working 
conditions  will  call  attention  to  a  possible  increase  of  the  per- 
centage of  slimes  or  fine  sand  present,  or  to  incomplete  draining. 
The  compact  nature  of  sand  in  a  collecting  vat  is  well  known. 
In  these  works,  as  already  stated,  treatment  is  not  carried  out 
until  the  sand  has  been  removed  from  the  collecting  vat  and 
transferred  to  the  leaching  vat.  One  advantage  gained  is  that 
the  subsequent  percolation  is  exceedingly  sure,  rapid,  and  thorough; 
125  tons  of  sand  will,  when  drained,  form  a  deposit  of  3  ft.  6  in. 
deep  in  a  30-ft.  collecting  vat.  After  the  complete  disintegration 
secured  by  the  excavating  process,  the  sand  is  again  broken  up 
and  blended  by  the  action  of  the  distributor,  with  the  result  that 
the  125  tons  will  produce  a  depth  of  5  ft.  8  in.  in  the  30-ft.  leaching 
vats  before  the  introduction  of  solution,  and  subsequently  settle 
8  in.  during  treatment.  Or  1  in.  depth  of  sand  in  the  collecting 
vat  will  produce  1.62  in.  in  the  treatment  vat  before  percolation, 
and  1.42  in.  afterward.  The  opportunity  secured  for  complete 
percolation  is  obvious. 

Those  familiar  with  the  chlorination  process  will  better  under- 
stand the  condition  of  this  sand  when  I  state  that  the  loose 
condition  which  is  secured  by  screening  the  charge  into  a  chlori- 
nation tank  is  here  obtained  by  means  of  the  Blaisdell  distributor. 
A  chlorination  tank,  20  ft.  in  diameter,  will  be  filled  to  a  depth 
of  7  ft.  3  in.  by  screening  in  an  80-ton  charge  of  roasted  concen- 
trates. This  depth  decreases  8  in.  by  subsidence  during  treatment. 


DISPOSAL  OF  TAILINGS  211 

The  charge  will  therefore  weigh  70  Ib.  per  cu.  ft.  before  and  77  Ib. 
after  treatment.  With  the  distributor  at  Virginia  City,  these 
weights  are  63  Ib.  and  71  Ib.  respectively.  In  the  first  instance, 
the  contents  settled  10.1  per  cent,  of  the  original  depth,  and  in 
the  second  instance  11.7  per  cent.  It  appears  from  this  that 
there  is  less  packing  from  the  distributor  action  than  from  the 
screening  method,  which  has  been  hitherto  the  most  perfect 
known. 

At  Virginia  City  the  yearly  cost  is  $84  per  electrical  horse- 
power, or  0.96c.  per  horse-power  hour.  An  addition  of  15  per 
cent,  should  be  made  to  cover  the  loss  in  the  motor-generator 
set.  This  brings  the  cost  up  to  l.lc.  per  horse-power  hour. 

The  total  power  used  by  this  system  for  the  double  handling 
of  125  tons  a  day  throughout  the  sand-house  creates  a  daily 
expense  made  up  of  the  following  items: 

Cents 

Discharging  collecting  vat  30.5  h.  p.  at  l.lc. 33.55 

Conveyors, NOB.  1,2 and 3,41.5     "     "  0.96e 39.80 

Distributing &5     "     "l.lc. 9.35 

DMdiargmg  leaching ?at..  11.5     "     "l.lc. 12.65 

Total  co*t  for  125  tons 95.35 

Total  cost  for  1  ton 0.763 

It  has  been  estimated  by  the  Blaisdell  company,  the  manu- 
facturers of  these  machines,  that  wear  of  disks  and  parts  will 
amount  to  $50  per  annum,  and  an  estimate  based  upon  the  past 
six  months1  use  shows  that  this  amount  is  correct.  To  this  may 
be  added  $30  for  grease,  waste,  oil,  etc.,  required  by  the  entire 
plant.  This,  then,  would  give  a  total  of  $80  per  annum  for 
maintenance,  or  21.9c.  per  day. 

The  daily  working  costs  may  be  tabulated  as  follows: 

Cento 

Power 95.35 

Supplies  and  war .' 21.90 

Labor -  60.00 

Total. 177.25 

Co*  per  too 1-415 

The  total  dally  cost  for  all  handling,  riHUlgiilg  of  solution*, 
and  general  sand-house  work  is  the  cost  of  power  and  maintenance, 
as  shown,  plus  the  total  time  of  the  operator  ($3  per  day) ,  making 
$4.17,  or  3.336e.  per  ton. 


212  METALLURGICAL  MILL  CONSTRUCTION 

If  the  works  had  to  be  enlarged  from  a  capacity  of  400  tons 
daily  to  a  capacity  of  1000  tons,  and  the  percentage  of  sand  con- 
tinued about  what  it  is  now,  the  only  change  required  for  enabling 
the  machines  to  handle  the  480  to  500  tons  of  sand  twice  in  the 
24  hours  would  be  to  replace  the  present  motor  upon  the  excavator 
by  one  of  greater  horse-power,  allowing  a  greater  feed  upon  the 
collecting  vats.  There  is  no  reason  why  an  excavator  should  not 
be  made  sufficiently  strong  to  discharge  100  tons  an  hour  from 
a  collecting  vat.  It  would,  of  course,  have  to  be  made  heavier 
than  the  present  machine,  which  is  intended  for  the  present  duty, 
and  which  has  fulfilled  all  requirements. 

The  introduction  of  the  Blaisdell  excavator  marks  a  new  era 
in  the  construction  of  cyanide  plants,  and  is  so  important  that  it 
will  be  worth  while  to  introduce  it  even  in  the  case  of  existing 
sand  plants  which  admit  of  the  necessary  modifications.  The 
reasons  for  its  use  are  strong  —  the  saving  of  gold  by  higher 
extraction,  and  the  reduced  cost  of  labor. 

El  Oro  Mining  &  Railway  Company,  of  Mexico,  is  now  erecting 
a  complete  cyanide  plant  for  the  new  100-stamp  mill.  The  por- 
tion of  the  works  for  treating  the  sands  consists  of  nine  collecting 
vats,  22  ft.  by  10  ft.,  served  by  one  Blaisdell  excavator,  and  of 
14  leaching  vats,  40  ft.  by  6  ft.,  in  two  rows,  served  by  one  exca- 
vator. By  arranging  a  series  of  Robins  belt  conveyors,  the  con- 
tents of  any  one  leaching  vat  can  be  transferred  to  any  other 
leaching  vat,  or  conveyed  direct  to  the  tailings  dump;  and  the 
capacity  of  excavators  and  of  the  belt  conveyors  is  100  tons  per 
hour.  The  estimated  cost  of  working  this  plant  in  Mexico,  at 
the  rate  of  200  tons  per  day,  is  3c.  per  ton,  and  it  requires  the 
services  of  two  men,  the  cost  of  power  being  taken  at  $10  (Amer- 
ican) per  horse-power  per  annum. 

The  conditions  under  which  the  tanks  are  filled  are  so  perfect 
that  only  one  treatment  is  required  for  complete  extraction,  as  is 
the  case  in  a  chlorination  tank,  because  the  sand  is  in  the  same 
condition  that  it  would  be  if  it  had  been  screened  into  the  tank. 

No  cyanide  solution  is  ever  run  into  the  collecting  tank,  as 
its  contents,  after  having  been  filled  from  the  battery,  are  allowed 
to  drain,  and  are  then  transferred  by  means  of  the  excavator 
directly  to  the  leaching  tank.  Therefore,  no  loss  of  gold  can  take 
place  from  cyanide  solution  having  been  introduced  into  the 
collecting  tank,  as  is  the  case  when  the  collecting  tank  is  filled 


DISPOSAL  OF  TAILINGS  213 

directly  from  the  battery,  and  gets  its  preliminary  treatment  of 
cyanide  solution  in  the  same  tank. 

At  Virginia  City,  as  much  as  50  per  cent,  of  gold  was  found 
dissolved  out  of  the  charge,  by  filling  into  a  collecting  tank  in 
which  the  previous  charge  had  received  a  preliminary  cyanide 
treatment,  and,  strange  to  say,  this  loss  continued  for  over  two 
weeks  after  the  use  of  cyanide  in  the  filling  of  the  vat  had  been 
discontinued.  While  no  trace  of  cyanide  could  be  obtained  at 
any  time,  still  the  loss  went  on,  until  after  two  very  anxious 
weeks  it  gradually  stopped.  This  occurred  on  two  different 
occasions.  At  first  it  was  attributed  to  an  excessive  amount  of 
ferric  salts  in  solution,  acting  possibly  as  a  solvent  for  gold;  but 
it  was  found  later  that  it  was  from  the  traces  of  cyanide  that 
could  not  possibly  be  detected  by  any  chemical  test. 

Mr.  Hennen  Jennings  and  Mr.  Butters  had  both  made  a 
series  of  determinations  at  Johannesburg  as  to  the  gold  in  the 
battery  water  from  this  source,  and  with  similar  results  —  gold 
was  invariably  found.  It  is  not  easy  to  state  the  exact  loss  from 
this  source,  but  that  it  is  a  source  of  loss  which  should  be  elimi- 
nated, I  think  all  engineers  and  metallurgists  will  agree.  The 
use  of  the  Blaisdell  excavator  reduces  the  number  of  vats  required 
to  produce  a  given  result,  even  with  the  separate  collecting  vats, 
as  rapid  percolation  takes  place  in  all  the  vats  used  for  leaching, 
while  at  present  only  one-half  the  vats  are  in  a  condition  for 
perfect  percolation. 

The  elimination  of  all  outside  labor  from  the  works  will  nat- 
urally appeal  to  every  one,  as  the  shiftsmen  with  this  apparatus 
can  transfer  the  contents  of  sand  tanks  and  discharge  them  when 
they  are  in  order,  and  need  not  wait  until  other  workmen  are 
ready.  Much  time  is  saved,  as  the  plant  is  much  more  elastic, 
and  nothing  waits  or  depends  upon  hand  labor. 


ECONOMY  IN  MILL  WATER 
BY  JESSE  C.  SCOBEY 

(December  10,  1903) 

With  no  running  or  surface  water  in  sight  or  available,  nine 
Wilfley  tables  were  operated,  during  the  year  1902,  at  Washington, 
Arizona,  in  a  plant  treating  100  tons  per  day,  and  requiring  a 
150-horse-power  steam  equipment. 

A  water  supply  was  accumulated  in  a  large  storage  tank 
before  starting  the  plant,  and  this  water,  when  the  plant  was 
running,  was  in  constant  circulation,  being  alternately  fouled 
and  cleaned  of  both  slimes  and  acid.  To  prevent  any  consump- 
tion in  excess  of  the  normal  allowance  was  vital,  as  it  would 
eventually  close  the  mill.  The  reserve  supply  generally  sustained 
the  minor  internal  losses,  and  only  on  a  few  occasions  was  it 
necessary  to  shut  down  from  an  actual  lack  of  water. 

The  final  improvements,  adopted  from  experience,  gave  a 
saving  of  97  per  cent,  of  the  water  in  circulation,  and,  in  view 
of  the  20  per  cent,  loss  admitted  to  be  made  in  the  South  African 
cyanide  plants,  this  loss  of  only  3  per  cent,  may  well  be  reviewed. 
The  comparison  in  no  way  criticizes  the  South  African  plants, 
as  the  widely  different  treatments  account  in  a  large  way  for  the 
discrepancy.  Mr.  Denny  said  recently,  in  the  Engineering  and 
Mining  Journal,  that  the  discharged  tailings  retain  only  10  per 
cent,  water,  and  in  this  he  means  the  sands  only,  else,  of  course, 
he  would  not  have  the  20  per  cent,  loss;  this  construction  puts 
the  entire  penalty  upon  the  separation  of  the  slimes,  as  in  my 
saving  of  97  per  cent,  the  sands  carried  25  per  cent,  water.  The 
stamp-mill  practice  produced  more  slimes  than  did  our  roller 
mill,  both  from  the  manner  of  crushing  and  the  method  of  screen- 
ing, using  in  the  stamps  30-mesh,  and  on  the  trommels  for  the 
rolls  a  12-mesh  cloth. 

That  the  20  per  cent,  loss  is  excessive  is  admitted,  when  it  is 
proposed  to  reduce  this  to  10  per  cent,  by  a  better  system  for 

214 


DISPOSAL  OF  TAILINGS  215 

saving  the  slimed  water,  in  the  use  of  20-ft.  circular  vats,  which 
step  is,  to  my  mind,  a  proper  one.  So  far,  the  system  proposed 
is  weak  in  the  vital  point  of  discharge,  which  must  be  over  the 
entire  periphery  and  must  not  be  drawn  from  one  point. 

The  entire  water  supply  at  Washington  was  obtained  by 
sinking  a  well,  from  which  was  run  a  drift  across  and  under  an 
arroyo,  draining  an  extensive  water-shed.  Tests  showed  that 
this  well  would  supply  7500  gallons  per  day  in  the  dry  season; 
of  course,  more  in  the  wet  season,  but  that  did  not  affect  the 
problem.  This  amount  was  considered  ample  when  properly 
used,  and  a  small  boiler  and  pump  were  installed  with  a  2-in. 
pipe  line,  to  deliver  this  water  to  the  plant,  1J  miles  distant. 

At  the  time  I  took  charge  of  the  plant,  all  machines  were  in 
place,  and  the  design  of  the  building  was  such  that  they  must  be 
connected  up  as  they  stood.  In  brief  outline,  the  ore  carried 
copper,  lead,  and  zinc  in  a  silicious  gangue,  heavy  with  garnet. 
It  was  crushed  in  rolls  to  12-mesh  and  roasted;  after  cooling,  it 
was  treated  magnetically,  and  about  20  per  cent,  of  the  ore  was 
lifted  as  a  copper  concentrate,  which  was  reduced  in  a  rever- 
beratory  furnace  to  copper  matte.  The  remaining  lead,  zinc,  and 
garnet  tails  were  submerged,  and  treated  on  tables  to  a  lead-zinc 
concentrate,  a  zinc-garnet  middling  and  tailings.  Each  of  the 
two  metallic  products  was  redressed  on  two  tables  to  shipping 
lead,  and  to  zinc  suitable  for  drying  and  subsequent  magnetic 
cleaning.  The  nine  tables  for  this  work  required,  in  feed  and 
wash  water,  900  tons  of  water  per  day,  or  216,000  gallons. 

The  table  floor  was  well  laid  in  hydraulic  cement,  draining  to 
the  center,  through  which  ran  an  open  cement  launder,  that 
carried  the  tailings  from  the  first  five  tables,  and  the  waste  water 
from  the  four  dressing-tables.  About  5  per  cent,  of  the  ore  was 
taken  out  as  a  lead  concentrate,  which  was  collected  in  special 
boxes,  from  which  the  overflow  water  was  discharged,  after 
passing  under  and  over  baffle-boards,  on  the  cement  floor,  from 
which  it  drained  into  the  main  artery.  The  concentrates  were 
shoveled  from  the  boxes  into  hemp  sacks,  and  when  first  sacked 
would  contain  25  per  cent,  moisture;  these  drained  to  15  per 
cent,  moisture  in  standing,  before  being  finally  removed  to  the 
shipping  platform.  The  15  per  cent,  moisture  in  5  tons  of  lead 
concentrates  made  a  loss  of  0.75  ton  or  180  gallons  per  24-hour 
day. 


216  METALLURGICAL  MILL  CONSTRUCTION 

The  zinc  dressing-tables  gave  about  15  per  cent,  of  the  ore  as 
material  to  be  dried  for  final  magnetic  work.  This  was  collected 
from  the  tables  to  an  automatic  drag,  similar  to  the  one  about 
to  be  described,  in  which  the  sands  were  separated,  giving  waste 
water  to  the  tailings  launder,  and  the  zinc,  with  25  per  cent, 
water,  to  the  drier,  where  the  water  was  lost  in  evaporation. 
The  25  per  cent,  moisture  in  15  tons  of  zinc  concentrates  made  a 
loss  of  water  of  3.75  tons,  or  900  gallons,  per  day.  This,  with 
the  loss  in  the  lead,  left  214,900  gallons  discharging  through  the 
main  launder,  with  recovery  of  which  we  were  mairity  concerned. 

The  extraction  of  copper,  lead,  and  zinc  left  about  60  per  cent, 
of  the  crude  ore  to  be  carried  in  suspension,  by  this  water,  to  a 
cement  pit,  from  which  it  was  raised  20  ft.,  a  head  sufficient  to 
allow  the  sands  to  be  drawn  off  and  the  cleared  water  to  be 
returned  by  gravity  to  the  head-tank  which  supplied  the  tables. 

Fig.  38  shows  the  means  of  accomplishing  the  separation 
of  the  sands  from  the  slime  water.  The  sand-box  is  in  the  form 
of  a  truncated  pyramid  inverted,  with  the  larger  triangle  at  the 
top,  having  a  7-ft.  base  and  10-ft.  altitude.  A  5-ft.  depth  of 
water  filled  the  box  to  within  4  in.  of  the  top.  All  sides  of  the 
box  slope  at  an  angle  of  60  deg.  toward  the  bottom  of  the  box, 
or  toward  the  edge  up  which  the  sands  are  dragged  at  an  angle 
of  30  deg.  In  this  way  all  material  settled  in  the  box  is  deposited 
under  the  drag  belt.  When  full,  the  settling  area  of  the  surface 
of  the  water  is  35  sq.  ft.  The  tailings  from  the  elevator  are 
discharged  into  the  sand-box  at  A,  where  the  false  back  a  extends 
across  the  box  and  to  within  18  in.  of  the  bottom,  allowing  a 
6-in.  space  for  the  full  width  of  the  back,  which  conducts  the  sand 
and  water  to  the  bottom  of  the  pyramid,  where  it  is  practically 
entered  at  the  apex,  and  under  the  bottom  pulley,  around  which 
the  drags  are  carried.  The  rising  current  is  thus  subjected  to  an 
enlarging  area,  increasing  as  the  square  of  the  distance  ascended, 
which  accordingly  reduces  the  velocity  in  like  proportion,  and 
effectually  drops  the  sand. 

From  the  surface  the  overflow  water  and  slimes  are  taken 
from  the  box  by  the  6-ft.  weir  B  over  the  edge  away  from  or 
opposite  to  the  sand  discharge.  This  wide  discharge  materially 
reduces  any  tendency  to  form  currents.  The  drag-belt  C  is 
12-in.  five-ply  rubber,  traveling  15  ft.  per  minute  over  the  foot 
pulley  z  and  the  head  pulley  c.  The  head  shaft  is  in  fixed  bearings, 


DISPOSAL  OF  TAILINGS 


217 


to  accommodate  the  gearing  necessary  to  drive  at  the  slow  speed, 
while  the  foot  shaft  is  held  loosely  in  its  position  by  wooden 
bearings,  as  is  the  practice  in  the  Joplin  mills.  These  bearings 
are  in  the  water  at  the  bottom  of  the  box  and  are  in  no  way 


FIG.  38.  —  Sand-box  in  Water-saving  Plant,  Washington  Mine. 

protected;  they  consist  simply  of  a  half-round  cut  in  the  end  of 
a  4x4-in.  hard-wood  block.  These  pieces  are  held  in  place, 
each,  by  two  bolts  in  slotted  holes  in  the  hickory,  with  just  suffi- 
cient tension  to  keep  the  belt  taut,  and  at  the  same  time  enabling 


218  METALLURGICAL  MILL  CONSTRUCTION 

it  to  be  taken  up  by  slightly  tapping  the  block  down  with  a  sledge. 
Our  experience  with  this  kind  of  bearing  in  such  a  place,  or  in 
the  foot  of  wet  elevators,  has  been  to  prove  its  superiority  over 
all  iron  and  babbitt  bearings,  arranged  either  bridged  or  over- 
hanging. It  is  much  easier  to  admit  that  sand  is  going  to  get 
into  your  bearings,  and  to  design  the  box  accordingly,  than  to 
make  fruitless  efforts  to  keep  it  out.  Under  the  above,  apparently 
severe,  test  the  wear  on  either  the  shaft  or  the  bearing  was  not 
disastrous,  after  six  months'  continuous  running.  A  hole  closed 
with  a  plug  in  the  bottom  of  the  box,  from  which  the  contents 
can  be  drawn,  is  convenient  in  case  of  clogging  or  breakage. 

The  belt  was  equipped  with  brackets  d,  bolted  14  in.,  center 
to  center,  to  which  the  drags  proper  (e)  were  bolted,  with  slotted 
holes  in  the  plate,  for  taking  up,  reversal,  or  renewal,  without 
changing  the  more  costly  bracket,  upon  which  there  is  little  wear. 
The  drag  was  constructed  especially  to  leave  a  space  between 
the  belt  and  the  plate,  so  that  when  leaving  the  water  the  current 
could  escape  over,  as  well  as  around  the  sides,  thus  lessening  any 
tendency  to  wash  away  the  sand  carried  on  the  drag.  From  the 
time  of  leaving  the  lower  pulley  until  discharging  the  gathered 
sand  at  the  top,  the  edge  of  the  plate  rested  on  the  floor  of  the 
edge  of  the  pyramid,  up  which  it  traveled,  protected  by  a  2-  by 
12-in.  piece,  that  could  be  renewed.  Acid  water  made  it  necessary 
that  the  bracket  and  drag,  as  well  as  all  elevator  cups  and  metal 
exposed  to  the  water,  should  be  made  of  copper;  consequently  we 
put  the  burden  of  the  wear  on  the  wood,  which  lasted  about  two 
months. 

All  the  sands  of  the  tailings  were  thus  dragged  over  the  point 
of  the  box,  and  some  2  ft.  beyond  the  surface  of  the  water,  allowing 
the  sands  to  drain,  after  which  they  were  discharged,  invariably 
containing  25  per  cent,  moisture,  to  a  small  accumulating  bin, 
to  be  taken  to  the  dump  in  wheelbarrows.  We  failed  in  an  effort 
to  handle  this  mass  by  a  belt  conveyor,  as  it  would  cling  to  the 
belt,  fouling  the  rollers  and  bearings,  and  quickly  destroying 
the  belt. 

The  water  delivered  from  the  sand-box  carried  about  10  per 
cent,  of  the  crude  ore  treated,  in  slimes,  while  the  sand  delivered 
was  50  per  cent,  of  the  ore.  The  loss  of  25  per  cent,  moisture,  in 
the  sands  going  to  the  dump,  amounted  to  12.5  tons  of  water  or 
3000  gallons  per  day.  This  loss  now  reduced  the  quantity 


TANK  AT  WASHINGTON  MILLS,  ARIZONA. 


OF  THE 

{    UNIVERSITY  ) 

OF 


DISPOSAL  OF  TAILINGS 


219 


going  to  the  slimes  tank  to  211,900  gallons,  contaminated  by  10 
tons  of  fine  slimes. 

A  photograph  shows  the  tank  in  question,  which  was  simply 
a  16-  by  16-ft.  standard  round  tank,  to  which  has  been  added  a 
false  lining  that  gives  the  interior  the  appearance  of  an  inverted 
cone,  with  sides  60  deg.  from  the  horizontal,  truncated  at  the 
bottom  of  the  tank  in  a  circle  of  2  ft.  diameter.  This  lining  is 
essential,  as  otherwise  the  settled  slimes  would  not  feed  regularly 
to  the  discharge.  No  especial  care  is  needed  in  putting  in  this 
lining,  as  it  is  supposed  to  fill  behind  with  water,  and  eventually 
with  slimes. 

Around  the  upper  rim  of  the  tank,  about  10  in.  down,  is  fitted 
a  10-in.  circular  launder,  enclosing  the  whole  circumference. 
This  was  most  expeditiously  made  by  forming  the  bottom  of  the 


Fio.  39.  —  Details  of  Scraper. 

launder  from  sections  sawed  from  a  2-in.  plank  to  fit  the  outside 
of  the  tank.  After  securing  these  in  place  temporarily,  the 
outside  of  the  launder  was  formed  by  tacking  to  the  2-in.  bottom 
the  lower  edge  of  a  10-in.  six-ply  rubber  belt,  which  was  easily 
formed  around  the  tank  in  one  piece.  This  was  quite  stiff  enough 
to  maintain  itself  erect,  especially  when  the  whole  was  incased 
by  an  ordinary  hoop-band  with  draw-nuts,  which  was  so  placed 
as  to  draw  the  belt  against  the  2-in.  bottom,  and  the  whole 
securely  against  the  tank. 

It  is  essential  to  have  the  overflow  water  drawn  evenly  over 
the  top  of  the  tank  from  all  parts  of  the  circumference,  and,  as 
the  tops  of  the  staves  are  irregular,  and  hard  to  dress  to  a  plane, 


220 


METALLURGICAL  MILL  CONSTRUCTION 


this  is  facilitated  by  nailing  around  the  top  a  0.5-in.  batten  on 
edge,  so  that  about  one-half  of  its  width  stands  above  the  ends 
of  the  staves;  this  thin  strip  is  easily  bent  around  the  tank,  and 
its  upper  edge  can  be  then  planed  down  to  an  exact  level,  when 


the  tank  is  filled  with  water;  also,  any  uneven  settling  can  be 
readily  remedied. 

In  the  center  of  the  bottom  of  the  tank  is  cut  a  6-in.  hole,  to 
which,  on  the  under  side,  is  bolted  a  6-in.  tee,  to  one  leg  of  which 
is  attached  a  gate- valve  that  can  be  opened  in  emergencies,  and 


DISPOSAL  OF  TAILINGS  221 

to  the  other,  by  reducers,  a  2-in.  hose,  which  is  carried  out  past 
the  chime  and  raised  some  8  ft.,  where  the  end  is  closed  with  a 
wooden  plug  in  the  center  of  which  is  a  0.5-in.  nipple. 

Supported  vertically  in  the  center  of  the  tank  is  a  long  tube 
or  box  open  at  both  ends,  12  by  12  in.  in  section,  extending  from 
above  the  water  level  down  to  within  2  ft.  of  the  bottom,  and 
directly  over  the  6-in.  slimes  outlet.  Into  the  upper  end  of  this 
tube  the  slime  and  water  from  the  sand  tank  is  introduced;  it  is 
delivered  at  the  bottom  at  the  apex  of  the  cone,  whence  it  rises 
evenly  without  irregular  currents.  With  the  velocity  decreasing 
as  the  square  of  the  ascension,  the  slimes  are  gradually  dropped 
and  are  drawn  continuously  from  the  0.5-in.  nipple. 

The  velocity  of  discharge,  and  consequently  the  quantity  of 
pulp  drawn  from  the  bottom  of  the  tank,  can  be  accurately 
gaged  to  suit  the  needs  by  raising  or  lowering  the  discharge  end 
of  the  hose,  and  thus  decreasing,  or  increasing,  the  head  under 
which  it  works.  This  is  an  important  detail,  as  no  valve  or 
jig-gate  can  be  set  to  a  small  discharge  of  slimes,  without  sooner 
or  later  causing  a  disastrous  stoppage  that  blocks  the  whole 
system.  In  our  instance  we  found  an  8-ft.  head  gave  us  a  desired 
discharge  of  thick  slimes,  of  about  the  consistency  of  molasses. 

Under  this  head,  and  with  a  0.5-in.  orifice,  clear  water  would 
have  been  discharged  at  a  rate  of  12,367  gallons  per  24  hours, 
using  the  coefficient  of  discharge  of  0.61.  In  our  case  the  friction 
of  the  thickened  slimes,  through  the  2-in.  hose  and  small  orifice, 
reduced  the  discharge  to  6500  gallons  per  day  of  slimes,  with 
two  parts  of  water  to  one  of  solid  matter. 

These  slimes  are  drier  than  those  recorded  by  Mr.  Denny  in 
his  practice,  as  4  to  1  from  the  first  operation,  and  I  think  this  is 
mainly  due  to  the  use  of  the  hose  discharge.  We  anticipated 
discharging  our  slimes  with  the  proportion  of  2  to  1,  but  as  there 
were  more  slimes  than  anticipated,  it  led  to  the  discovery  that 
when  reduced  to  this  thickness  they  settled,  and  gave  a  covering 
of  clear  water  in  time  remarkably  short  in  view  of  their  former 
obstinacy.  Accordingly  we  were  led  to  re-treat  them,  which 
should  have  been  done  by  the  same  system,  but  being  driven  to  act 
quickly,  we  made  a  6-  by  8-  by  6-ft.  V-box,  which,  taking  so  small 
a  stream  of  pulp,  discharged  clear  water,  and  settled  slimes  in  the 
bottom  as  a  thick  mud,  from  where  it  was  drawn  intermittently 
by  an  attendant  who  took  this  as  one  of  his  miscellaneous  duties. 


222  METALLURGICAL  MILL  CONSTRUCTION 

Ten  tons  of  slime  tailings  were  thus  discharged  here,  that 
would  average  about  one  part  water  to  one  of  solid  matter,  which 
caused  a  loss  of  10  tons  of  water,  or  2400  gallons  per  day.  In 
summation  there  are  losses  as  follows: 

Gallons 

5  tons  of  lead  concentrates 180 

15  tons  of  zinc  concentrates 900 

50  tons  of  coarse  tailings 3000 

10  tons  of  slime  tailings 2400 

Total 6480 

In  such  a  climate  the  evaporation  may  be  considered,  but  it 
is  not  as  much  as  is  generally  supposed,  and,  in  our  case,  we 
estimated  as  nearly  as  possible  that  we  were  losing  6500  gallons 
per  day,  distributed  as  above.  With  216,000  gallons  in  circula- 
tion, this  loss  of  6500  gallons  represents  a  loss  of  only  3  per  cent. 

Various  attempts  have  been  made  to  claim  a  saving  equal  to 
this,  by  the  use  of  huge  and  cumbersome  V-boxes,  as,  notably, 
at  Cananea,  but,  from  casual  observation,  it  could  hardly  be 
credited. 

I  have  noticed  that,  where  apparently  muddy  water  was 
flowing  over  a  wide  weir,  there  was  generally  a  thin  film  of  clear 
water  on  the  surface.  Whether  this  is  due  to  any  property  of 
the  surface  of  water  peculiar  to  the  surface  only,  as  in  the  capillary 
attraction  shown  on  the  sides  of  a  vessel  of  water,  or  on  the  bead 
over  the  gager's  hook,  I  do  not  know,  but  to  draw  clear  water 
from  a  light  slime  it  is  necessary  to  reduce  the  velocity  of  discharge 
by  extending  the  cross-section  of  discharge  to  its  limit  of  breadth, 
so  that  the  depth  of  the  cross-section  of  discharge  reduces  the 
water  to  a  practical  film;  which  brings  us  to  the  same  thing. 

In  the  case  of  our  16-ft.  tank,  the  loss  of  6500  gallons  left 
209,500  gallons  in  circulation,  which  was  cleared  in  24  hours. 
As  our  discharge  was  over  the  entire  circumference  of  the  upper 
rim  of  the  tank,  this  was  equivalent  to  discharging  over  a  50-ft. 
weir.  Such  a  quantity  of  water  discharging,  in  this  time,  over  a 
50-ft.  weir  would  flow  with  a  depth  or  head  of  only  0.1875  in. 
This  was  the  depth  of  our  film,  as  near  as  it  was  practical  to 
measure.  Simple  hydraulic  formulas  will  show  that  from  a  head 
of  0.1875  in.,  under  the  above  conditions,  we  will  have  a  velocity 
of  approach  of  0.42  ft.  per  second,  or  1500  ft.  per  hour. 

These  figures  I  consider  important  for  a  justifiable  anticipa- 


DISPOSAL  OF  TAILINGS  223 

tion  of  good  work.  I  know  that  the  tank  would  do  nothing  like 
the  same  work  if  the  discharge  were  drawn  from  a  12-in.  opening 
at  any  one  point  of  the  rim.  If  this  should  be  done,  we  would 
have  a  12-in.  weir,  which,  to  discharge  the  above  amount  of 
water  in  the  same  time,  would  require  a  depth  or  head  of  2.4  in., 
which  would  draw  from  below  what  I  would  call  the  safe  film, 
and  would  also  create  a  velocity  of  1.6  ft.  per  second,  or  5760  ft. 
per  hour. 

In  this  latter  case,  the  depth  over  the  weir  would  be  13  times 
as  great,  and  the  velocity  of  approach  would  be  four  times  as 
great,  which  would  again  seem  to  accentuate  the  fact  that  the 
depth  of  discharge  from  the  tank  is  of  more  importance  than  the 
velocity. 


REMOVAL  OF  SAND  FROM  WASTE  WATER 

BY  J.  E.  JOHNSON,  JR. 

(December  31,  1903) 

I  have  read  with  the  greatest  interest  the  article  of  Messrs. 
Butters  and  Crank  in  the  Engineering  and  Mining  Journal  of 
December  5,  and  that  of  Jesse  Scobey  in  the  issue  of  December  10, 
both  dealing  with  the  matter  of  handling  sand,  especially  its 
removal  from  streams  of  running  water.  The  reason  for  this 
interest  is  that  I  had  occasion  to  deal  with  this  problem  about 
seven  years  ago,  although  under  slightly  different  conditions. 
The  problem  and  its  solution  were  both  presented  in  an  article 
in  the  Transactions  of  the  American  Institute  of  Mining  Engineers 
entitled  "  An  Apparatus  for  the  Removal  of  Sand  from  the  Waste 
Water  of  Ore- Washers,"  to  which  all  who  are  interested  in  this 
subject  are  respectfully  referred.  It  may  not  be  amiss,  however, 
as  nearly  six  years  have  elapsed  since  the  publication  of  that 
paper,  to  go  briefly  over  the  ground  there  covered,  and  outline 
the  solution  of  the  problem  reached. 

The  problem  was  one  of  the  removal  of  sand  and  fine  iron  ore, 
all  of  which  passed  through  a  14-mesh  screen  from  the  waste 
water  of  an  iron-ore  washer.  The  material  varied  from  the  size 
of  the  mesh  down  to  the  finest  silt  and  clay,  held  in  suspension  in 
the  water,  but  a  great  deal  of  it  was  an  iron-ore  sand  of  about 
the  size  of  ordinary  beach  sand,  such  as  probably  most  of  your 
readers  familiar  with  mill  practice  will  recognize  as  passing  through 
a  14-mesh  screen.  This  material  was  so  heavy  that  its  removal 
become  almost  a  necessity,  since  it  clogged  the  long  troughs  used 
to  carry  the  water  to  the  settling  ponds,  and  caused  them  to  fill 
up  so  that  they  overflowed  unless  the  inclination  was  excessive, 
in  which  case  the  hight  lost  was  a  serious  consideration.  More- 
over, it  was  recognized  that  the  greater  part  of  this  material  was 
iron  ore,  and  it  was  hoped  that  a  method  of  treating  it  so  as  to 
produce  a  material  of  commercial  value  would  eventually  be 
found,  and  this  has  since  actually  been  done.  Moreover,  the 
bulk  of  this  material  in  the  settling  ponds  was  most  objectionable, 

224 


DISPOSAL  OF  TAILINGS  225 

filling  them  up  with  great  rapidity.  The  quantity  of  material  of 
this  nature  handled  is  about  50  tons  in  10  hours,  and  the  water 
from  which  it  is  removed  amounts  to  about  750  gallons  per  minute. 
None  of  the  ordinary  solutions  of  the  problem  which  had  then 
been  made  seemed  to  suit  the  conditions  without  promising 
endless  wear,  and,  in  fact,  in  adopting  the  traveling-belt  plan  of 
operations,  Mr.  Scobey  states  plainly  that  wear  at  certain  points 
is  to  be  provided  for,  and  that  it  is  much  better  to  admit  this 
and  make  preparations  accordingly  in  the  first  place.  The  general 
plan  of  the  sand-shoveler  devised  by  me  assumed  as  its  funda- 
mental principle  that  its  bearings  should  be  kept  away  from  the 
sand  and  water.  It  was  obvious  that  a  vertical  wheel  would 
carry  sand  over  and  drop  it  down  on  its  own  bearings.  It  was 
equally  obvious  that  a  horizontal  wheel  would  not  remove  the 
sand  from  the  water  at  all.  It  was  not  obvious  by  any  means, 
but  was  eventually  found  to  be  the  case,  that  a  wheel  with  an 
inclined  axis  was  capable  of  elevating  the  sand  and  of  being 
supported  so  that  no  sand  or  water  whatever  reached  its  bearings. 
The  central  idea  of  reducing  the  velocity  of  the  water,  so  that  it 
would  drop  the  material  it  carries  in  virtue  of  its  velocity,  is  not 
unlike  that  of  Mr.  Scobey 's,  but  instead  of  the  dragging  action 
used  by  him,  a  true  shoveling  action  is  employed.  Almost  the 
only  defect  of  the  machine  is  the  great  difficulty  of  representing 
its  action  by  a  drawing,  or  even  by  a  photograph.  The  axes  of 
the  wheels,  of  which  there  are  two,  stand  at  45  deg.  each  side  of 
the  vertical  line,  and  the  general  plane  of  the  shovel  blades 
stands  at  approximately  45  deg.  with  the  axes  of  the  wheels,  so 
that  in  their  lowest  position  they  are  approximately  horizontal, 
and  in  their  uppermost  position  they  are  approximately  vertical. 
The  consequence  is  that  they  go  into  the  sand  at  a  slight  angle 
from  the  horizontal,  pick  it  up  from  just  above  the  bottom  of 
the  settling  box,  or  tank,  in  which  they  work,  move  it  diagonally 
through  the  water,  at  the  same  time  raising  in  front  and  tipping 
down  behind,  an  action  which  has  become  pronounced  when  the 
blades  emerge  from  the  water,  so  that  the  water  picked  up  by 
them  runs  off  the  back  edge  while  the  sand  stays  on  the  front  edge. 
The  diagonal  motion  carries  them  gradually  clear  of  the  sides  of 
the  troughs  and  the  angle  with  the  horizontal  is  constantly 
increasing,  so  that  when  the  blade  is  in  its  highest  position  it  is 
vertical,  and  the  sand  has  nothing  to  do  but  slide  off  clear  of  the 


226  METALLURGICAL  MILL  CONSTRUCTION 

edge  of  the  trough.  The  action  of  the  machine  both  in  delivering 
more  of  the  sand,  and  delivering  it  in  a  drier  condition,  is  greatly 
enhanced  by  making  the  shovels  of  perforated  material.  It  is, 
of  course,  impracticable  to  get  any  material  with  holes  fine  enough 
to  retain  the  sand  and  yet  have  the  material  stiff  enough  to  support 
the  stresses  upon  it.  Accordingly  the  shovels  are  made  of  double 
thickness,  the  bottom  one  of  J-in.  steel  thickly  perforated  with 
f-in.  holes,  the  upper  one  of  about  No.  16  zinc  perforated  with 
T^  in.  holes.  The  fact  is  familiar  to  all  that  sand  will  flow  as 
long  as  it  has  water  in  it,  but  sets  very  firmly  when  it  becomes 
dry,  and  this  construction  of  the  shovels  takes  advantage  of  this 
fact,  since  the  water  drains  out  of  the  sand  almost  instantly  owing 
to  the  large  surface  exposed  for  drainage,  with  the  result  that  the 
sand  sets  quite  solidly,  like  wet  beach  sand,  and  does  not  display 
any  tendency  to  run  over  the  back  edge  of  the  shovel,  as  it  some- 
times does  with  solid  blades.  The  drive  of  the  machine  is  through 
a  horizontal  shaft  carrying  a  worm  into  which  worm-gears  on  the 
upper  extremity  of  each  wheel-shaft  engage,  so  that  there  are  but 
three  moving  parts  in  the  whole  machine.  As  to  durability,  the 
machine  requires  a  new  set  of  zinc  covers  on  the  blades  about 
every  year  and  a  half,  and  the  worm  which  drives  it  was  renewed 
about  a  week  ago  for  the  first  time  in  about  six  years.  The  zinc 
sheets  for  the  shovel  blades  cost  something  less  than  50c.  each, 
and  the  worm  is  an  ordinary  cast-iron  worm  worth  not  over  $5  at 
the  outside.  These  are  all  of  the  repairs  which  have  been  put  on 
the  machine  in  its  7J  years  of  constant  operation,  without  any 
attention  whatever  except  an  occasional  oiling. 

It  will  be  seen  that  the  machine  has  to  remove  its  sand  from 
a  very  much  larger  quantity  of  water  proportionately  than  the 
apparatus  of  Mr.  Scobey,  as  750  gallons  of  water  per  minute  in 
24  hours  amount  to  1,080,000  gallons,  whereas  Mr.  Scobey  had 
only  about  214,000  gallons,  and  the  sand  removed  by  this  machine 
is  about  50  tons  in  10  hours  or  120  tons  in  24  hours,  where  his 
handled  50  tons  in  24  hours;  or  about  900  gallons  of  water  per 
ton  of  sand  in  our  practice  and  about  4280  gallons  per  ton  of 
sand  in  Mr.  Scobey's  case.  As  the  energy  of  the  water  varies  as 
the  square  of  its  velocity,  it  is  obvious  that  the  recovery  of  the 
sand  from  the  water  would  have  been  very  much  easier  in  his  case 
than  in  ours.  The  capacity  of  the  machine,  is,  to  be  sure,  some- 
what greater  than  needed  by  Mr.  Scobey,  but  even  if  this  size  of 


DISPOSAL  OF  TAILINGS  227 

machine  were  used,  its  size  would  be  an  advantage,  in  that  the 
velocity  of  water  through  the  settling  tank  would  be  so  much  the 
less  that  the  extraction  of  sand  would  be  the  more  complete.  I 
feel  sure  that  this  would  be  the  case.  In  regard  to  cost  of  appa- 
ratus, Mr.  Scobey  gives  no  figures,  but  presumably  there  would 
not  be  a  great  deal  of  difference  either  way.  When  it  comes  to 
repairs  and  ease  of  maintenance,  however,  I  am  convinced  that 
the  sand-shoveler  would  come  out  far  in  the  lead. 

In  regard  to  the  Virginia  City  plant  described  by  Messrs. 
Butters  and  Crank,  it  seems  a  pity  that  resort  to  so  elaborate  an 
apparatus  should  have  been  had  to  accomplish  the  end  desired. 
As  far  as  the  distributor  is  concerned,  there  is  nothing  to  be  said, 
since  that  is  not  a  very  complex  machine  and  should,  from  its 
description,  be  a  very  efficient  one;  but  the  method  of  recovering 
the  sand  from  the  water,  while  it  may  work,  is  enormously  expen- 
sive in  first  cost,  and  more  or  less  so  in  maintenance  and  in  power 
requirements.  It  will  be  seen  that  the  amount  of  sand  treated 
in  24  hours  is  just  about  the  capacity  of  the  sand-shoveler  as 
given  above,  and  had  the  sand-shoveler  been  installed  in  an  en- 
largement of  the  flume  bringing  the  tailings  from  the  waste  dumps 
to  the  mill,  the  sand  could  all  have  been  removed  from  the  flume  at 
one  point  without  the  necessity  of  settling  tanks  at  all,  and  it  could 
have  been  carried  by  a  much  simpler  system  of  conveyors  directly 
to  the  distributor.  The  attendance  required  would  have  been 
less,  the  work  would,  as  far  as  can  be  determined  from  the  de- 
scription of  the  writers,  have  been  done  absolutely  as  well,  and 
the  saving  in  the  first  cost  would  have  been  enormous. 

Considering  the  great  number  of  cyanide  plants,  and  other 
plants  which  have  to  handle  tailings,  now  in  existence,  and  the 
growing  strictness  of  the  powers  that  be  in  regard  to  contamination 
of  streams,  this  problem  of  handling  material  of  this  class  and 
removing  it  from  running  water  becomes  one  of  considerable 
importance.  No  less  an  authority  than  Dr.  E.  D.  Peters  said, 
during  the  discussion  of  my  paper  before  mentioned,  that  this 
machine  should  have  a  field  of  usefulness  in  cyanide  and  similar 
plants,  and  while  practically  no  effort  has  been  made  to  introduce 
it  into  this  field,  the  growing  interest  in  the  subject  and  the 
growing  demand  for  something  of  this  kind  seemed  to  me  a  suffi- 
cient justification  for  calling  the  attention  of  the  milling  fraternity 
at  large  to  this  very  simple  and  inexpensive  machine. 


DISPOSITION  OF  TAILINGS 

(December  17,  1903) 

Question.  —  At  a  pyrites  mine,  situated  in  a  populous  district, 
it  is  proposed  to  erect  a  dressing-plant  of  about  100,000  tons 
yearly  capacity.  If  no  special  precautions  are  taken,  most  of 
the  finer  tailings  will  pass  into  a  small  river,  5  to  6  km.  long, 
and  thence  into  a  larger  river  on  which  is  situated  a  valuable 
salmon  fishery,  and  which  is  bordered  by  cultivated  ground 
usually  overflowed  by  the  river  when  in  flood.  To  prevent  heavy 
damages,  it  is,  therefore,  necessary  that  the  water  from  the  small 
river  be  kept  free  from  tailings.  It  is  proposed  to  make,  near 
the  dressing-plant,  a  series  of  large  settling-boxes  provided  with 
filters,  having  openings  of  5  to  10  mm.,  in  order  to  catch  the 
pyrites;  and  also  to  make  one  or  more  settling  basins  in  the  small 
river.  It  has  also  been  proposed  to  use  filter-presses.  As  I  am 
not  sure  that  these  measures  would  be  sufficient,  I  should  be 
obliged  for  some  advice  on  this  subject.  The  quantity  of  water, 
with  the  tailings  from  the  dressing-plant,  will  be  from  15  to  20 
gallons  per  minute.  The  flow  in  the  small  river  is  150  to  200 
gallons  per  second.  —  H.  H. 

Answer.  —  This  is  a  matter  on  which  you  should  take  special 
professional  advice  and  make  some  experiments.  If  you  do  that, 
you  ought  to  be  able  to  determine  what  danger  there  may  be 
and  how  it  may  be  eliminated.  We  can  only  give  you  some 
general  ideas. 

:  The  question  of  stream  pollution  frequently  comes  up.  In 
the  Engineering  and  Mining  Journal  of  Dec.  5,  1903,  page  864, 
our  San  Francisco  correspondent  referred  to  the  fight  now  going 
on  in  Calaveras  county,  Cal.,  between  the  miners  and  the  farmers, 
the  latter  complaining  that  the  tailings  from  the  copper  ore 
dressing  works  at  Campo  Seco  are  polluting  the  water  of  the 
Mokelumne  River,  destroying  the  fish,  and  injuring  vegetation 
along  the  banks.  The  State  Fish  Commission  investigated  the 
matter  and  found  that  nothing  harmful  was  passing  into  the 

228 


DISPOSAL  OF  TAILINGS  229 

river  from  the  copper  mines,  and  that  although  the  water  was 
discolored  by  material  from  the  Gwin  gold  mine,  where  much 
blue,  slaty  rock  is  crushed,  no  fish  had  been  killed,  nor  had  fields 
which  had  been  irrigated  with  the  water  suffered  any  damage  at 
all.  Samples  of  the  water  tested  chemically  disclosed  the  presence 
of  no  free  acid. 

The  muddy  water  discharged  from  dressing  works  can  be 
clarified  perfectly;  it  is  not  necessary  to  resort  to  filter-presses, 
which  would  be,  in  all  probability,  far  too  expensive.  It  is  not 
necessary  even  to  let  the  clarified  water  go  at  all.  The  prime 
essential  is  to  provide  settling  reservoirs  of  sufficient  capacity. 

At  the  mill  of  the  Bullion-Beck  &  Champion  Mining  Company, 
at  Eureka,  Utah,  crushing  200  tons,  per  24  hours,  of  ore  containing 
lead  and  copper  minerals,  the  entire  drainage  was  collected  in  a 
reservoir  of  40,000  sq.  ft.  area,  the  sides  of  which  were  built  of 
coarse  tailings  and  made  water-tight  by  the  finest  slimes.  The 
clear  water  was  drawn  off  from  this  reservoir  into  a  tank  36  by 
20  ft.  in  area,  7  ft.  deep,  whence  it  was  pumped  at  the  rate  of 
100  to  125  gallons  per  minute  into  a  receiving  tank,  where  it 
arrived  almost  free  from  sediment.  No  water  was  lost  except  by 
evaporation.  At  the  washery  of  the  Longdale  Iron  Company,  in 
Virginia,  the  coarse  sand  is  removed  from  the  mill  discharge  by 
means  of  a  mechanical  device,  and  the  slimy  water  is  then  run 
into  reservoirs,  through  the  banks  of  which  it  is  allowed  to  filter; 
it  escapes  perfectly  clear.  This  is  done  to  avoid  pollution  of  a 
stream. 

Assuming  that  some  such  system  be  adopted  in  your  case,  a 
factor  to  be  considered  is  the  presence  of  acids  or  soluble  salts  in 
the  water  from  your  works,  which  may  arise  from  the  use  of 
mine  water  or  by  fresh  water  taking  up  soluble  matter  from  the 
ore;  and,  if  present,  whether  they  would  be  in  sufficient  quantity 
to  injure  the  fish  and  vegetation;  and  if  so,  might  they  not  be 
removed  by  some  simple  system  of  neutralization  or  precipitation. 
It  would  appear  advisable  to  clarify  your  mill  water  before  you 
allowed  it  to  run  into  the  small  river  at  all,  because  then  you 
would  have  a  very  much  smaller  quantity  to  deal  with. 


PART  VII 
MISCELLANEOUS 


RUBBER  AND  RUBBER  BELTING 

(March  9,  1901,  and  February  3,  1906) 

Data  as  to  the  weight  of  rubber  belting  are  seldom  to  be  found 
in  the  catalogues  of  belt  manufacturers,  chiefly  because  it  is  so 
variable,  depending  upon  the  different  conditions  of  manufacture. 
Belting  consists  of  two  parts,  the  duck  and  the  rubber.  The 
former  is  used  in  different  weights  in  making  belts  of  the  same 
ply,  and  the  weight  of  the  rubber  part  is  not  only  affected  by  the 
percentage  and  character  of  the  adulterants  that  are  used,  but 
the  weight  of  pure  rubber  is  variable.  Speaking  generally,  a 
good  8-in.  four-ply  belt  ought  to  weigh  about  1  Ib.  per  linear  foot. 
Probably  all  the  rubber  that  is  used  is  adulterated  to  some  extent, 
now  more  than  ever  in  view  of  the  high  prices  which  have  been 
established  by  the  greatly  increased  demand  for  rubber  and  the 
diminishing  supply.  This  has  led,  among  other  things,  to  an 
active  business  in  the  recovery  of  rubber  from  old  material,  gum 
shoes  and  the  like.  Even  the  South  American  and  African  natives 
who  supply  the  crude  material  have  their  tricks  in  the  trade,  one 
of  which  used  to  be  to  incorporate  a  stone  or  two  in  each  cake 
of  the  crude;  but  the  buyers  circumvented  that  by  cutting  open 
the  cakes  upon  purchase. 

Para  rubber  is  the  standard.  Rubber  dealers  have  learned, 
however,  to  mix  other  rubbers  in  such  ways  and  proportions  as 
to  produce  an  article  which  closely  resembles  the  Para  and  would 
probably  deceive  any  one  but  an  expert.  The  adulterants  com- 
monly used  in  the  manufacture  of  rubber  goods  are  chalk,  gypsum, 
calcined  magnesia,  asphaltum,  barytes,  litharge,  talc,  lampblack, 
and  zinc  white.  Manufacturers  are  naturally  reticent  as  to  which 
of  these  they  use  and  in  what  proportions.  In  a  recent  law  case 
in  England  it  was  elicited  from  one  of  the  witnesses  that  the 
material  of  which  carriage  tires  were  made  was  composed  of 
48.5  per  cent,  pure  rubber,  5.4  per  cent,  sulphur,  6.7  per  cent, 
barytes,  7.6  per  cent,  litharge,  20.7  per  cent,  chalk,  9.1  per  cent, 
steatite  (talc),  and  2  per  cent,  lampblack.  From  this  analysis 

233 


234  METALLURGICAL  MILL  CONSTRUCTION 

commercial  rubber  appears  to  be  more  of  a  mineral  substance 
than  it  is  a  vegetable.  The  sulphur  shown  by  the  analysis  is  of 
course  residual  from  the  process  of  vulcanizing  and  is  not  properly 
to  be  considered  as  an  adulterant. 

Zinc  white  is  largely  used  as  an  adulterant  for  rubber.  The 
recent  large  increase  in  the  consumption  of  that  substance  in  the 
United  States  is  said  to  be  due  to  the  rubber  manufacturers 
rather  than  to  the  paint  trade.  It  is  claimed  by  some  manufac- 
turers that  the  quality  of  rubber  is  improved  for  certain  purposes 
by  the  introduction  of  some  of  the  above-mentioned  mineral 
substances,  its  durability  being  in  some  way  increased,  and  there 
appears  to  be  more  or  less  truth  in  their  claims.  Elastic  bands 
are  one  of  the  purest  forms  in  which  rubber  is  used  and  every  one 
knows  how  rapidly  they  lose  their  strength  and  break.  Inciden- 
tally it  may  be  remarked  that  an  adulterant  has  recently  been 
found  that  can  be  used  to  an  important  percentage  in  rubber  for 
elastic  bands  without  apparently  affecting  their  elasticity. 

Some  specifications  for  belting  call  for  a  tenor  in  pure  rubber 
of  45  to  55  per  cent.  However,  the  tensile  strength  of  a  good 
rubber  belt  is  very  much  in  excess  of  any  pull  to  which  it  is  likely 
to  be  subjected,  though  in  this  connection  it  should  be  noted 
that  the  weakest  part  is  at  the  lacing,  where  the  material  must 
be  strong  enough  to  prevent  the  lacing  from  tearing  through  the 
relatively  short  distance  between  the  holes  and  the  ends.  Al- 
though the  mineral  adulterants  may  not  injure  and  may  really 
improve  the  rubber  employed  in  the  manufacture  of  belting, 
their  effect  on  rubber  to  be  used  for  chemical  and  perhaps  other 
purposes  may  be  deleterious  and  should  be  well  investigated. 
This  may  be  done  by  incineration  of  a  sample  and  chemical 
analysis  of  the  ash. 

The  average  weight  of  a  good  four-ply  rubber  belt,  7  in. 
wide,  is  about  16  oz.  per  linear  foot.  A  very  light  7-in.  four- 
ply  belt  may  weigh  as  little  as  12  oz.  per  linear  foot;  a  very 
heavy  belt  of  tho  same  dimensions  may  weigh  as  much  as  20  oz. 
The  weight  of  rubber  belting  varies  to  some  extent  with  the 
quality  of  the  raw  material  and  the  time  of  the  year  when  manu- 
factured, and  it  is  consequently  impossible  to  give  exact  figures. 
Some  inferior  rubber  belts  weigh  more  than  first-class  products 
because  of  the  use  of  adulterated  rubber,  the  adulterations  em- 
ployed being  as  a  general  thing  heavier  than  the  rubber  itself. 


MISCELLANEOUS  235 

The  nature  of  these  adulterants  is  a  secret  of  the  trade.  It 
is  well  known,  however,  that  zinc  oxide,  barytes,  litharge,  chalk, 
gypsum,  talc,  magnesia,  asphaltum,  and  lampblack  are  used  for 
this  purpose.  Experts  in  the  manufacture  of  goods  are  able 
to  identify  adulterated  rubber  by  its  appearance  and  physical 
characteristics.  The  extent  to  which  adulteration  has  been  prac- 
tised may  be  determined  from  the  comparative  weight  of  the 
ash  of  various  samples  after  incineration. 

The  best  rubber  belting  is  made  with  32-oz.  duck.  A  7-in. 
four-ply  belt  made  of  32-oz.  duck  weighs  about  20  oz.  per  lin- 
ear foot;  a  7-in.  four-ply  belt  weighing  16  oz.  per  linear  foot 
is  made  from  28  to  30-oz.  duck;  a  belt  of  the  same  dimensions 
weighing  only  12  oz.  per  linear  foot  would  have  only  26-oz. 
duck. 


COAL-DUST  FIRING 
BY  C.  O.  BARTLETT 

(December  31,  1903) 

Three  conditions  are  requisite  for  the  successful  combustion 
of  coal  in  dust  form,  viz.:  uniformity  of  moisture,  uniformity  in 
size  of  grain,  and  proper  regulation  of  the  supply  of  air.  Uni- 
formity in  moisture  is  best  attained  by  drying  the  coal.  As  to 
size,  it  is  best  reduced  so  as  to  pass  an  80-mesh  screen.  Control  of 
the  air  supply  is  best  secured  by  introducing  it  by  means  of  a  fan 
or  blower.  If  these  three  conditions  are  met,  perfect  combustion 
of  the  coal  may  be  attained,  with  the  results  of  no  black  smoke, 
no  cinders  and  very  little  ashes,  and  a  saving  of  practically  40 
per  cent,  in  the  consumption  of  coal. 

For  the  drying  of  the  coal,  a  rotary  cylinder,  heated  externally, 
is  recommended.  In  some  cases  the  products  of  combustion  are 
allowed  to  pass  first  on  the  outside  of  the  drier,  and  then  through 
the  inside.  When  this  is  done,  it  is  safe  to  reckon  an  evaporation 
of  10  Ib.  of  water  per  pound  of  coal  burned.  Otherwise,  the  ratio 
will  be  about  8:  1.  Estimating  on  a  basis  of  drying  40  tons  of 
coal  per  day  and  an  expulsion  of  5  units  of  moisture,  with  coal  at 
$2  per  ton,  the  cost  of  drying  will  be  less  than  12c.  per  ton.  With 
a  good  mill,  requiring  about  25  horse-power,  4  tons  of  dry  coal 
can  be  pulverized  per  hour.  The  kinds  of  mills  at  present  in  use 
for  this  purpose  are  the  French  buhr  mill,  the  Huntington,  and 
the  ball-  and  tube-mills.  It  is  safe  to  reckon  on  a  cost  of  lOc. 
per  ton  for  pulverizing.  The  cost  of  elevators,  conveyors,  bins, 
running  the  blower  or  feeder,  repairs  and  renewals,  and  interest 
on  the  investment,  ought  not  to  come  to  more  than  lOc.  per 
ton,  making  the  total  cost  only  32c.  per  ton  of  dry  coal.  The 
approximate  cost  of  a  plant  for  firing  4  tons  of  coal-dust  per 
hour  is  as  follows:  Drier,  $1500;  pulverizer,  $2500;  feeders,  $1000; 
conveyors,  elevators,  bins,  etc.,  $2000;  total,  $7000.  Besides  the 
economy  in  coal,  dust-firing  presents  the  further  advantage  of  a 

236 


MISCELLANEOUS  237 

saving  in  labor.  Laborious  handling  of  coal  into  the  furnace  is 
obviated;  there  is  not  more  than  one-third  as  much  ashes  to  be 
handled,  and  there  are  no  cinders  at  all.  The  economical  applica- 
tion of  coal-dust  firing  implies,  however,  the  use  of  a  fairly  large 
quantity  of  coal.  It  would  not  pay  to  put  in  the  necessary  plant 
for  a  consumption  of  less  than  1  ton  per  hour. 

In  coal-dust  firing,  the  arrangement  of  the  combustion  chamber 
of  the  furnace  is  an  important  consideration.  In  one  experiment 
the  Rowe  system  was  used,  which  consists  in  blowing  the  pulver- 
ized coal,  by  means  of  an  ordinary  fan,  against  an  arch,  burning 
the  coal  in  suspension.  The  arch  becomes  very  hot  and  imme- 
diately ignites  the  coal;  when  the  proper  quantity  of  air  is  used, 
combustion  is  perfect.  It  was  found  that  a  2-oz.  pressure  was 
best  for  this  purpose.  In  order  to  withstand  the  very  high 
temperature,  special  brick  should  be  used  in  the  construction  of 
the  arch.  There  is  a  German  invention  for  protecting  the  arch 
with  a  lining  made  of  carborundum  dust,  which,  it  is  said,  will 
withstand  the  highest  temperature  until  worn  away  mechanically. 


INTERNALLY  FIRED  BOILERS 

(August  8,  1903) 

Internally  fired  boilers  of  the  Scotch  type  are  finding  increased 
use  in  the  United  States  for  general  purposes  of  steam  generation. 
Many  of  the  newer  metallurgical  plants  are  equipped  with  this 
form  of  boiler.  It  is  somewhat  more  expensive  than  the  ordinary 
horizontal  return  tubular  boiler,  allowing  for  the  brick  setting  of 
the  latter,  which  the  internally  fired  boiler  does  not  require,  but 
the  additional  cost  is  not  so  high  as  to  offset  the  advantages  in 
many  cases. 

Among  the  advantages  of  the  internally  fired  boilers  is  safety 
against  explosion.  It  is  said  that  there  is  no  case  on  record  of 
the  explosion  of  a  boiler  of  this  type.  The  boiler,  not  being 
enclosed  in  brick  work,  is  subject  to  inspection  from  the  outside 
at  all  times,  and  the  plates  of  the  shell  are  not  exposed  to  the 
direct  heat  of  the  fire,  wherefore  there  is  but  little  deterioration 
in  the  plates  of  the  outer  shell  or  the  joints  thereof.  The  danger 
of  bagging  sheets,  which  is  apt  to  occur  in  any  externally  fired 
boiler,  due  to  an  accumulation  of  scale  or  sediment  on  the  fire- 
sheet,  is  also  eliminated.  The  lower  part  of  the  internally  fired 
boiler  is  not  exposed  to  the  fire  at  all,  and  any  deposits  collecting 
in  the  form  of  a  slush  or  mud  are  readily  blown  out.  It  is  claimed 
also  that  the  tendency  for  scale  to  adhere  to  the  furnace  is  reduced 
to  an  extent  that  will  not  cause  any  trouble,  the  expansion  and 
contraction  of  the  corrugated  surface  of  the  furnace  having  the 
effect  of  loosening  the  scale.  With  respect  to  the  small  fire-tubes, 
the  conditions  of  the  internally  fired  boiler  are  substantially  the 
same  as  those  of  the  ordinary  horizontal  return  tubular  type. 

The  chief  advantages  of  the  internally  fired  boiler  are  economy 
in  fuel  and  lower  cost  of  maintenance.  A  saving  in  the  latter 
respect  may  be  expected  in  almost  all  cases.  There  is  no  brick 
setting  to  maintain,  and,  as  stated  above,  there  is  less  likelihood 
of  deterioration  in  some  of  the  parts  of  the  shell.  The  saving  in 
fuel  is  determined  by  the  fact  that  the  fire  is  entirely  surrounded 

238 


MISCELLANEOUS  239 

by  water  to  be  heated,  wherefore  no  loss  is  suffered  through 
radiation  from  the  fireplace.  With  many  kinds  of  fuel  this  may 
constitute  a  rather  important  advantage.  This  advantage  may 
be  offset,  however,  with  poor  grades  of  coal  by  the  limited  volume 
of  the  fireplace,  which  does  not  afford  sufficient  space  for  the 
gases  to  mix  in  order  to  insure  complete  combustion  before  the 
temperature  is  cooled  below  the  ignition  point. 

The  internally  fired  boiler  is  attractive  because  of  its  neat 
appearance  in  place  and  the  simplicity  of  erecting  it,  the  boiler 
being  delivered  in  a  complete  condition  and  requiring  nothing 
but  a  few  small  piers  for  its  foundation.  The  floor  space  required 
is  also  somewhat  less  than  for  the  ordinary  return  tubular  type. 

The  advantages  of  the  cylindrical  boiler,  with  internal  corru- 
gated fire-box,  and  its  superiority  to  the  ordinary  locomotive  type 
boiler  have  been  recognized  by  railroad  men.  The  use  of  such  a 
boiler  for  a  locomotive  was  first  suggested  by  Bela  Ambrosovics 
on  the  Hungarian  State  railroads  about  fifteen  years  ago.  The 
idea  was  taken  up  by  Herr  Lentz,  on  the  Prussian  State  railroad, 
and  Herr  Scheffler,  on  the  Saxon  State  railroads,  about  1891,  and 
at  about  the  same  time  George  S.  Strong  used  it  in  an  experi- 
mental locomotive  built  by  the  Rhode  Island  Locomotive  Works. 
Mr.  Strong's  idea  was  not  a  success,  but  its  failure  was  due  to 
other  causes  than  the  fire-box.  The  plan  was  taken  up  again  by 
Cornelius  Vanderbilt,  Jr.,  on  the  New  York  Central,  some  two 
years  ago,  and  since  that  time  boilers  of  this  type,  with  corrugated 
fire-boxes,  have  been  built  for  a  number  of  roads,  and  have  proved 
highly  successful.  We  may  add  that  this  type  of  boiler  is  espe- 
cially adapted  for  the  use  of  liquid  fuel,  which  is  becoming  quite 
common  in  California  and  in  the  Southwest. 


ACCIDENTS  TO  MOTORS  AND  DYNAMOS l 

BY  A.  C.  CORMACK 

(October  3,  1903) 

An  analysis  of  the  breakdowns  occurring  during  the  last  four 
years  to  several  thousand  motors  and  dynamos,  ranging  in  size 
from  0.5  horse-power  to  800  kilowatts,  has  been  made.  The 
machines  taken  into  consideration  had  been  working  under  con- 
ditions better  than  the  average,  and  consequently  the  results 
obtained  must  be  regarded  as  considerably  above  the  average. 
Motors  driving  coal-cutting  machines  have  not  been  included. 

The  relative  frequency  with  which  various  portions  of  dynamos 
and  motors  were  damaged  in  breakdowns  was  as  follows :  Mechan- 
ical portions  :  broken  shafts,  2.35  per  cent.;  binders  and  fasteners, 
9.40  per  cent.;  bearings,  8.60  per  cent.;  other  mechanical  parts, 
4.70  per  cent.;  total,  25.05  per  cent.  Brush-gear,  connections, 
terminals,  etc.  :  Failure  of  brush  insulation,  2.35  per  cent.;  con- 
nections and  terminals,  3.10  per  cent.;  mechanical  portion  of 
brush  gear,  1.56  per  cent.;  total,  7.01  per  cent.  Field  magnet 
coils  :  Coils  burnt  out,  5.50  per  cent.;  coils  earthed,  3.10  per  cent.; 
coils  gone  altogether,  1.56  per  cent.;  total,  10.16  per  cent.  Arma- 
tures :  Coils  short-circuited  and  burnt  out,  29  per  cent.;  coils 
earthed  (that  is,  failure  of  insulation  of  frame),  19.50  per  cent.; 
breakage  of  wire,  15.60  per  cent.;  joint  failures,  8.60  per  cent.; 
binders  burnt,  3.10  per  cent.;  driving  horns,  2.35  per  cent.;  total, 
33.60  per  cent.  Commutators  :  Failure  of  insulation,  10.15  per 
cent.;  mechanical  failures,  10.95  per  cent.;  surface  fusion,  12.50 
per  cent.;  total,  33.60  per  cent. 

When  several  parts  failed  in  a  single  breakdown,  each  is 
included  in  the  above  summary,  except  those  cases  where  the 
failure  of  one  part  was  certain  to  follow  the  failure  of  another. 
Of  the  accidents  in  which  the  field  magnet  coils  were  damaged, 

i  Abstract  of  a  paper  on  "  Electric  Plant  Failures,  Their  Origin  and  Pre- 
vention/' read  before  the  British  Institution  of  Civil  Engineers,  1903. 

240 


MISCELLANEOUS  241 

the  larger  number  were  cases  in  which  the  insulation  between 
the  coil  and  core  gave  way.  The  failures  due  to  the  entire  burning 
out  of  the  coils,  i.e.,  arcing  from  series  to  shunt  on  the  same  coil, 
or  arcing  between  two  separate*  coils,  occurred  most  frequently 
in  bipolar  machines,  where  the  coils  often  touch.  The  failure  of 
armatures  is  the  most  serious  danger,  usually  taking  the  form  of 
a  burning  out  of  coils.  Coils  earthed  were  generally  due  to 
destruction  of  the  insulation.  Commutators  are  frequently  dam- 
aged, failure  of  insulation  being  the  most  frequent  trouble.  The 
mechanical  failure  of  commutators  is  due  to  bursting,  fracture  of 
commutator-lugs  and  failure  of  keying. 

The  points  of  origin  of  breakdown,  together  with  the  percent- 
ages of  the  frequency  with  which  the  various  parts  failed,  were 
as  follows:  Mechanical  portions  :  Shafts,  0.78  per  cent.;  bearings, 
8.60  per  cent.;  general,  1.65  per  cent.;  total,  11.03  per  cent. 
Brush-gear,  leads,  and  terminals:  Mechanical,  3.90  per  cent.; 
insulation,  2.35  per  cent.;  leads  and  terminals,  2.35  per  cent.; 
total,  8.60  per  cent.  Field  magnets  :  failure  of  coil  insulation, 
7.80  per  cent.;  breakage  of  wire,  0.78  per  cent.;  total,  8.58  per 
cent.  Armatures  :  Core  and  slot  insulation,  12.50  per  cent.;  end 
insulation  (that  is,  separating  bridges),  5.50  per  cent.;  coil  insula- 
tion, 11.70  per  cent.;  joints,  7  per  cent.;  fasteners  and  binders, 
1.65  per  cent.;  binder  insulation,  7.80  per  cent.;  driving  horns, 
1.65  per  cent.;  total,  47.80  per  cent.  Commutators:  Insulation, 
9.40  per  cent.;  fastening  and  keying,  5.50  per  cent.;  total,  14.90 
per  cent.  Starters,  4.70  per  cent.;  unknown,  3.13  per  cent.; 
various,  1.56  per  cent. 

Shaft  breakdowns  were  caused  generally  by  the  armatures 
coming  out  of  center  through  wear  of  the  bearings.  Bearings 
frequently  wear  upward,  this  sometimes  occurring  in  cases  where 
the  armature  has  been  placed  nearer  the  top  of  the  race  than 
the  bottom  in  order  that  the  upward  pull  of  the  magnets  may 
relieve  the  pressure  on  the  bearings.  Owing  to  the  liability  of 
this  wear  to  escape  attention,  it  is  somewhat  dangerous.  Com- 
mutators were  responsible  for  14.9  per  cent,  of  the  breakdowns. 
Commutator  breakdowns  are  of  two  classes.  The  first,  in  which 
the  insulation  has  failed,  occurs  most  frequently  between  the 
bars  and  supporting  rings,  and  results  often  in  the  burning  out 
of  the  armature  windings.  Defective  fastening  and  keying  of 
the  commutator  constitute  the  second  class  of  accidents  to  which 


242  METALLURGICAL  MILL  CONSTRUCTION 

this  part  of  the  machine  is  subject.  When  the  keying  is  defective 
the  commutator  is  driven  by  the  armature  wires,  and  sometimes 
the  commutator  and  the  armature  have  a  slight  relative  motion 
on  the  shaft.  This  causes  breakages  of  the  wires  joining  the 
armature  to  the  commutator. 

The  conclusions  which  have  been  reached  as  to  the  causes  of 
breakdowns  are  summarized  as  follows:  Constructional:  Bad 
design,  18.36  per  cent.;  perishing  of  insulation,  7.40  per  cent.; 
bad  workmanship,  13.60  per  cent. ;  total,  39.36  per  cent.  Con- 
ditional: Overloading,  1.37  per  cent.;  over-rating  1.56  per  cent.; 
unsuitable,  0.78  per  cent.;  total,  3.71  per  cent.  Maintenance: 
Dust  and  damp,  7.40  per  cent.;  rough  usage,  1.56  per  cent.  De- 
fective attention  other  than  above,  22.50  per  cent.;  total,  31.46 
per  cent.;  accidental  and  unavoidable,  with  reasonable  care  in 
construction  and  working,  7.05  per  cent.;  unknown,  13.10  per 
cent.;  caused  by  faults  in  accessories,  5.48  per  cent. 

Comparatively  few  of  the  faults  were  found  in  the  mechanical 
portions  of  the  machine.  These  usually  took  the  form  of  insuffi- 
cient keying,  bad  arrangement  of  bearings,  and  other  ordinary 
mechanical  defects.  There  is  a  tendency  to  design  machines 
having  higher  rises  of  temperature  than  experience  has  shown  to 
be  compatible  with  reasonable  durability  of  the  machine.  Defects 
from  dust  occur  most  frequently  in  semi-closed  motors,  for 
which  the  provision  for  cleaning  is  usually  insufficient. 


ALLOYS  FOR  BEARING  PURPOSES l 

BY  G.  H.  CLAMER 

(September  12,  1903) 

A  good  alloy  for  bearing  purposes  must  consist  of  at  least  two 
constituents,  namely,  a  hard  one  to  support  the  load  and  a  soft 
one  to  act  as  a  plastic  support  for  the  harder  grains.  If  the 
bearing  were  always  in  perfect  adjustment  with  respect  to  the 
journal  a  hard,  unyielding  alloy  would  be  the  best,  since  the  harder 
the  alloy  the  lower  is  the  coefficient  of  friction,  generally  speaking. 
It  is  found,  however,  that,  owing  to  the  imperfect  nature  of  the 
surface  in  practice,  a  hard,  unyielding  alloy  which  cannot  mold 
itself  to  the  irregularities  of  the  journal  will  cause  a  concentration 
of  pressure  upon  a  few  high  spots,  with  the  result  of  rapid  heating 
and  abrasion.  Soft  metal  bearings,  on  the  other  hand,  are  apt 
to  give  rise  to  unduly  rapid  wear  of  the  journals;  but  whether 
this  be  due  to  the  imbedding  of  grit  in  the  bearing  surfaces,  or 
to  the  fact  that  the  metal  itself  has  a  dragging  nature,  is  uncer- 
tain. The  excessive  collar  wear  of  journals  is,  however,  undoubt- 
edly caused  by  the  lead  lining  lapping  out  of  the  fillets. 

The  cheapest  of  the  white  metal  alloys  is  lead  and  antimony. 
These  metals  alloy  in  all  proportions,  but  the  eutectic  mixture  is 
composed  of  approximately  87  per  cent,  lead  and  13  per  cent, 
antimony.  This  has  been  adopted  by  the  Pennsylvania  Railroad. 
As  the  percentage  of  antimony  increases  the  alloys  become  more 
brittle;  with  more  than  25  per  cent,  antimony  they  are  unsafe  to 
use.  Charpy  considers  that  the  alloys  containing  between  15 
and  25  per  cent,  antimony  are  the  best  constituted  for  bearings, 
the  free  antimony  forming  the  necessary  hard  constituent  im- 
bedded in  the  plastic  eutectic.  However,  it  may  be  pointed  out 
that  the  alloys  containing  free  lead  also  possess  the  necessary 
structure  of  a  hard  constituent,  in  this  case  the  eutectic,  imbedded 

i  Abstract  of  a  paper  in  the  Journal  of  the  Franklin  Institute,  1903, 
CLVI,  pp.  49-77. 

243 


244  METALLURGICAL  MILL  CONSTRUCTION 

in  the  more  plastic  lead;  although  the  friction  of  such  alloys  is 
higher  than  that  of  those  containing  an  excess  of  antimony,  the 
wear  is  much  less.  Lead  is  the  best  wear-resisting  metal  known; 
with  additional  antimony,  increasing  hardness  and  brittleness, 
the  wear  augments,  owing  to  the  breaking  off  of  the  harder 
particles. 

Tin  added  to  lead  and  antimony  imparts  rigidity  and  hardness 
without  increasing  the  brittleness.  It  is  desirable,  therefore, 
when  high  pressures  have  to  be  carried.  Babbitt  metal,  which  is 
regarded  as  the  standard  of  excellence,  consists  of  89.1  per  cent. 
of  tin,  7.4  per  cent,  of  antimony  and  3.7  per  cent,  of  copper. 
It  is  the  most  expensive  of  the  white  metals,  and  in  the  majority 
of  cases  may  be  replaced  by  a  cheaper  alloy. 

With  respect  to  the  bronzes,  composed  of  copper,  tin,  and  lead, 
it  is  found  that  the  rate  of  wear  diminishes  with  decrease  of  tin 
and  with  increase  of  lead.  Dudley's  "Ex.  B."  alloy,  consisting 
of  78  per  cent,  copper,  7  per  cent,  tin,  and  15  per  cent,  lead,  was 
formerly  believed  to  represent  the  minimum  of  tin  and  the  maxi- 
mum of  lead  possible  in  practice  without  danger  of  liquation  of 
the  lead  occurring  in  the  mold.  Experiments  have  since  shown, 
however,  that  while  a  certain  proportion  of  tin  is  necessary  to 
prevent  liquation  of  the  lead,  and  also  to  give  the  alloy  sufficient 
tiompressive  strength,  a  larger  proportion  is  very  detrimental. 
Alloys  containing  5  per  cent,  tin  and  30  per  cent,  lead  have  been 
produced  without  difficulty,  but  if  the  tin  exceeded  6.10  per 
cent.,  castings  containing  30  per  cent,  lead  could  not  be  obtained, 
and  if  the  tin  exceeded  7  per  cent.,  not  more  than  20  per  cent, 
of  lead  could  be  introduced  under  practical  conditions.  An  alloy 
finally  invented  was  composed  of  64  per  cent,  copper,  5  per  cent, 
tin,  30  per  cent,  lead,  and  1  per  cent,  nickel.  This  is  known  as 
"plastic  bronze."  Nearly  4,000,000  Ib.  of  it  have  been  success- 
fully made  during  the  last  three  years,  in  castings  weighing 
from  1  Ib.  to  over  1000  Ib.  The  castings  are  sharp  and  clean 
and  can  be  readily  machined. 


COST  OF  SMALL  POWER  PLANTS 

(September  5,  1903) 

Some  recent  bids  on  high  speed  engines  of  100  to  300  i.  h.  p., 
by  high-class  manufacturers,  have  ranged  from  9c.  to  12c.  per  lb., 
f.  o.  b.  factories,  the  former  price  being  on  the  larger  engines 
and  the  latter  on  the  smaller.  These  prices  figure  out  to  $11@$18 
per  i.  h.  p.  An  engine  of  150  horse-power  costs  about  $12.50. 
A  good  Corliss  engine  of  the  same  power  is  obtainable  for  about 
$12  per  i.  h.  p.,  or  7.5c.  per  lb.  Good  horizontal,  return  tubular 
boilers  of  about  100  horse-power,  designed  for  steam  pressure  of 
100  lb.,  can  be  had  for  $7@$8  per  horse-power.  Internally  fired 
boilers  of  the  same  capacity  cost  about  $12.50  per  horse-power, 
but  the  difference  is  partially  offset  by  the  less  cost  of  setting. 
The  water-tube  boilers  are  the  most  expensive  in  first  cost.  A 
good  feed- water  heater  can  be  purchased  for  about  $1  per  boiler 
horse-power.  The  total  cost  of  a  steam  power  plant  of  300 
horse-power  capacity  will  be  about  $50  per  horse-power.  .  .; 


The  ordinary  pile-driver  cannot  be  very  much  improved  in 
the  matter  of  capacity.  It  is  true  that  steam  drivers  have  been, 
and  are  being,  successfully  used;  but  the  shorter  period  taken1  in 
driving  does  not  materially  affect  the  total  capacity  of  a  crew. 
The  main  cause  of  the  limited  output  in  driving  piles  is  the  length 
of  time  necessary  to  adjust  the  pile  and  the  machine  to  the  posi- 
tion required;  this  is  irrespective  of  the  type  of  driver  used,  and 
the  rapidity  of  action  of  the  latter  has  so  slight  an  effect  upon 
the  total  time  spent  that  the  increase  in  the  number  of  piles 
driven  per  day  is  very  small. 


245 


CONSTRUCTION  OF  WOODEN  WATER  TANKS 

(December  5,  1903) 

Water  tanks  for  fire  protective  purposes,  which  often  do  not 
receive  ordinary  care  and  supervision,  frequently  collapse,  some- 
times with  considerable  damage.  The  fire  underwriters  have 
been  led,  therefore,  to  study  the  causes  of  such  collapses  and  the 
remedy.  Their  conclusions  are  of  value  in  specifying  the  proper 
construction  for  wooden  tanks  for  any  purpose. 

The  most  frequent  cause  of  collapse  is  corrosion  of  the  hoops. 
The  ordinary  hoop  is  a  flat  wrought-iron  band,  J  to  J  in.  thick, 
and  of  varying  widths.  They  are  seldom  painted,  either  before 
or  after  putting  on,  and  are  subject  to  corrosion  both  from  the 
outside  and  the  inside.  Outside  corrosion  is  easily  observed,  but 
not  so  the  inside  corrosion;  and  the  real  condition  of  the  hoops  is 
seldom  known  until  collapse  occurs.  Inside  corrosion  is  due 
chiefly  to  moisture,  which  works  into  and  through  the  staves  of 
the  tanks.  Many  hoops  corrode  sufficiently  to  fall  off  by  their 
own  weight.  The  only  way  to  determine  the  condition  of  flat 
hoops  is  to  reinforce  the  tank  with  additional  hoops,  and  then 
remove  the  old  ones  for  examination. 

Flat  hoops,  when  properly  cared  for,  will  give  satisfactory 
service,  but  round  hoops  are  much  to  be  preferred.  With  round 
hoops,  corrosion  from  the  inside  acts  only  on  a  small  surface,  as 
compared  to  the  flat  hoop,  and  ordinary  inspection  will  detect 
the  corrosion  before  it  has  progressed  sufficiently  to  weaken  the 
hoop.  Round  hoops  have  the  further  advantage  that  swelling 
of  the  tank  is  less  likely  to  burst  the  hoops,  since  a  round  hoop 
will  indent  itself  into  the  wood. 

Hoops  should  be  made  of  wrought  iron  of  good  quality,  with 
tensile  strength  of  not  less  than  50,000  Ib.  per  sq.  in.  In  deter- 
mining the  size,  a  factor  of  safety  of  5  or  6  should  be  used,  and 
allowance  should  be  made  for  the  swelling  of  the  staves,  which 
will  strain  the  hoops  more  than  the  actual  pressure  of  the  water 
in  the  tank.  Hoops  should  never  be  less  than  J  in.  in  diameter. 
They  should  be  made  without  welds,  and  should  be  thoroughly 
painted  before  and  after  erection. 

246 


PIPE  LINE  CONSTRUCTION 

(October  10,  1903) 

There  are  said  to  be  approximately  25,000  miles  of  pipe  line 
laid  for  the  conveyance  of  natural  gas  in  the  United  States. 
These  are  of  various  sizes,  ranging  from  2  in.  in  diameter  up  to 
36  in.  For  the  transportation  of  large  quantities  of  gas,  or  even 
comparatively  small  quantities  when  the  line  is  a  long  one  and 
pumping  is  not  resorted  to,  the  pipes  have  to  be  of  considerable 
diameter.  Thus  the  transportation  of  4,000,000  cu.  ft.  of  gas 
per  24  hours  (166,667  ft.  per  hour)  a  distance  of  20  miles,  with 
intake  pressure  of  200  Ib.  and  discharge  of  20  lb.,  requires  a  6-in. 
pipe.  Reckoning  25,000  cu.  ft.  of  gas  as  equivalent  to  2000  lb. 
of  coal,  4,000,000  cu.  ft.  of  gas  per  24  hours  corresponds  to  only 
160  tons  of  coal.  The  construction  of  a  6-in.  line  will  probably 
cost  about  $4750  per  mile,  or  $95,000  for  20  miles.  Allowing 
only  10  per  cent,  for  interest  and  depreciation,  the  daily  charge 
is  $9500  -s-  365  =  $26,  which  would  be  equivalent  to  paying  for 
the  carriage  of  coal  at  0.8c.  per  ton-mile.  When  the  intake 
pressure,  i.e.,  the  pressure  at  the  gas  wells,  falls  below  200  lb., 
either  a  pumping  plant  must  be  put  in  or  a  larger  line  must  be 
put  down.  Remoteness  from  sources  of  the  gas  therefore  increases 
the  cost  of  the  latter  very  rapidly.  The  construction  of  a  pipe 
line  of  large  diameter  is  an  expensive  undertaking,  the  larger 
sizes  exceeding  in  cost  that  of  a  first-class  railway  line. 

Pipe  lines  for  the  transportation  of  natural  gas  are  commonly 
constructed  of  wrought-iron  pipe,  technically  known  as  "line 
pipe,"  which  is  tested  up  to  1500  lb.  Line  pipe  is  made  with 
longer  couplings  than  ordinary  pipe.  The  standard  sizes  range 
from  2  in.  to  12  in.  diameter.  The  smaller  pipe  lines,  say  10  in. 
in  diameter  or  less,  are  usually  laid  with  the  standard,  screw- 
joint  line  pipe,  but  lately  plain-end  pipe  with  couplings  and  rubber 
packing  has  become  very  popular,  and  is  to  a  large  extent  taking 
the  place  of  screw- joint  pipe,  it  being  equally  cheap  in  first  cost 
and  more  readily  laid.  The  pipe  line  should  be  buried  under 

247 


248  METALLURGICAL  MILL  CONSTRUCTION 

ground,  so  that  the  distance  from  the  surface  of  the  ground  to 
the  top  of  the  pipe  will  be  18  to  20  in.  This  puts  the  line  out 
of  the  way  and  makes  it  comparatively  free  from  the  expansive 
and  contractive  force  to  which  it  would  be  subject  if  it  were 
exposed  on  the  surface  of  the  ground  to  the  direct  heat  of  the 
sun.  The  ditching  is  not  very  expensive;  in  ordinary  soil  it 
ought  not  to  cost  much  more  than  6c.  per  lineal  foot.  The  pipe 
should  be  well  protected  with  coal  tar  on  the  outside  before 
laying.  Expansion  joints  should  be  put  in  from  time  to  time, 
say  at  one-half  mile  intervals,  and  also  a  certain  number  of 
gate- valves  and  tees  to  permit  connections  to  be  made  at  points 
where  they  may  be  required.  A  well-laid  pipe  line  suffers  com- 
paratively little  depreciation  in  value,  and  the  pipe,  after  having 
been  in  the  ground  for  four  or  five  years,  may  be  taken  up  and 
sold  at  a  discount  of  only  15  to  25  per  cent,  from  the  first  cost, 
according  to  the  demand  at  the  time.  Second-hand  pipe  in  large 
quantity  is  always  more  or  less  in  request. 

Sizes  of  pipe  from  10  in.  to  2  ft.  in  diameter  are  frequently 
laid  with  the  Converse  joint,  in  connection  with  which  the  pipe 
has  plain  ends,  the  connections  being  made  by  heavy  cast-iron 
sleeves,  or  hubs,  fitted  with  molten  lead,  which  is  calked  into 
the  space  between  the  pipe  and  the  sleeve.  This  joint  has  the 
disadvantage  that  the  packing  may  be  loosened  by  the  settling 
of  the  pipe  and  the  movement  due  to  changes  in  temperature. 
However,  by  the  addition  of  a  rubber  packing  pressed  against  the 
outside  of  the  joint  by  means  of  iron  clamps,  a  satisfactor3T 
connection  can  be  made.  Pipe  lines  of  this  construction  have 
operated  under  a  pressure  of  more  than  300  Ib.  per  square  inch. 
For  pipe  lines  of  more  than  2  ft.  diameter,  cast-iron  water  pipe  or 
riveted  steel  pipe  are  put  down.  A  line  of  riveted  steel  pipe, 
36  in.  diameter,  extending  20  miles  southward  from  Pittsburg,  Pa., 
cost  approximately  $50,000  per  mile.  At  present,  Pittsburg  is 
receiving  gas  from  points  in  West  Virginia  more  than  100  miles 
distant,  while  the  lines  which  supply  Chicago,  Toledo,  and  Cleve- 
land are  considerably  longer,  the  gas  in  some  cases  being  conducted 
200  miles. 


TRANSPORTATION  OF  GAS  BY  PIPE  LINES 

(February  4,  1904) 

Question.  —  On  page  541,  issue  of  the  Engineering  and  Mining 
Journal  of  October  10,  I  notice  an  article  entitled  "Pipe-line 
Construction,"  from  which  I  quote  as  follows:  "Thus  the  trans- 
portation of  4,000,000  cu.  ft.  of  gas  per  24  hours  (166,667  ft.  per 
hour)  a  distance  of  20  miles  with  intake  pressure  of  200  Ib.  and 
discharge  of  20  Ib.  requires  a  6-in.  pipe." 

I  am  very  much  interested  in  the  matter  of  transportation  of 
gas  through  pipe  lines  under  high  pressure,  and  have  made  quite 
a  study  of  what  information  I  have  been  able  to  secure  on  this 
subject;  from  all  of  which  I  have  worked  up  a  formula  which 
seems  to  me  to  be  the  best  and  most  complete  of  anything  that 
I  have  found,  although  there  seems  to  be  a  great  poverty  of 
information  on  this  subject.  Working  the  problem  in  the  above 
quotation  by  this  formula,  and  on  the  assumption  that  the  natural 
gas  referred  to  has  a  specific  gravity  of  0.50,  the  results  should 
widely  differ  from  those  stated  by  you,  and  I  therefore  beg  to 
inquire  if  the  information  given  is  the  result  of  observation  from 
actual  practice,  or  whether  it  is  worked  from  a  formula.  If  so, 
I  will  be  pleased  to  learn  the  formula  used.  —  L. 

Answer.  —  The  capacity  of  the  pipe  line  under  the  conditions 
specified  was  computed  by  the  formula 


I 

in  which  Q  is  the  quantity  of  gas  in  cubic  feet  per  hour,  d  the 
diameter  of  the  pipe  in  inches,  P  and  p  the  absolute  pressure  of 
the  gas  in  pounds  at  the  inlet  and  outlet,  respectively,  and  I  the 
length  of  the  pipe  in  miles.  The  factor  41  is  a  constant.  It  is 
sometimes  taken  as  42  and  sometimes  as  40.  It  should  really 
be  a  trifle  more  than  41,  being  based  on  the  figure  3000  when 
I  is  stated  in  feet;  extracting  the  square  root  of  5280  and  dividing 
3000  by  the  quotient  gives  41.1  +  .  This  formula  is  used  by 
some  engineers  to  arrive  at  the  volume  of  gas  of  0.65  specific 

249 


250  METALLURGICAL  MILL  CONSTRUCTION 

gravity.  According  to  it,  a  1-in.  pipe,  20  miles  long,  with  pressure 
of  200  —  20  Ib.  (above  atmospheric)  would  deliver  about  1959.4 
cu.  ft.  per  hour.  A  6-in.  line  would  deliver  95  times  as  much, 
or  186,143  cu.  ft.  This  is  more  than  would  be  worked  out  directly 
by  the  formula  for  a  6-in.  line,  the  result  of  which  would  be 
171,495  cu.  ft.  This  is  because  the  multipliers  determined  by 
experiment  show  that  the  capacity  of  a  pipe  increases  actually 
in  a  little  greater  ratio  than  the  square  root  of  the  fifth  power 
of  the  diameter. 

Another  formula  that  is  employed  is 


Dl 

in  which  D  is  the  specific  gravity  of  the  gas;  save  for  that,  and 
the  use  of  the  factor  40  instead  of  41,  it  is  the  same  as  the  first 
formula,  but  the  introduction  of  the  factor  of  specific  gravity, 
which  is  a  decimal,  in  the  denominator  under  the  square  root 
sign  gives  a  larger  quotient  and  consequently  higher  results. 

Both  these  formulas  give  very  much  higher  results  than  those 
which  are  commonly  given  for  the  flow  of  coal  gas  in  pipes,  which, 
according  to  various  authorities,  are  as  follows: 


King 
Q  —  1350  t  /  ^ 

Molesworth 
O      1000  4  /  ^h 

Gill 
0—1291  i/     ^h 

y        V  si 

H5            *WV   »  / 

V    si 

In  these  d  is  the  diameter  of  the  pipe  in  inches,  h  the  pressure 
in  inches  of  water,  s  the  specific  gravity  of  the  pipe,  and  /  the 
length  of  the  pipe  in  yards. 

Gill's  formula  is  said  to  be  based  on  experimental  data,  and 
to  make  allowance  for  obstructions  by  tar,  water,  and  other 
bodies  tending  to  check  the  flow  of  gas.  An  experiment  made  in 
London  with  a  4-in.  pipe,  6  miles  long,  with  gas  of  0.398  specific 
gravity  and  3-in  pressure,  gave  a  result  which  corresponded 
closely  with  Molesworth's  formula.  (See  Kent's  "  Mechanical 
Engineer's  Pocket-book/'  p.  657.) 

The  figure  0.50  is  rather  low  for  the  specific  gravity  of  natural 
gas,  which  is  commonly  assumed  at  0.60  to  0.65.  The  specific 
gravity  of  methane  is  0.533,  while  that  of  ethane  is  1.034.  Ac- 
cording to  S.  A.  Ford,  the  specific  gravity  of  the  gas  found  in 
the  vicinity  of  Pittsburg,  Pa.,  was  about  0.65,  as  a  rule. 


MAKING  PIPE  JOINTS 

(April  4,  1904) 

At  the  meeting  of  the  American  Society  of  Heating  and 
Ventilating  Engineers,  Jan.  19,  1904,  there  was  a  discussion  of 
the  question:  "In  making  screwed  joints,  is  it  better  to  use  some 
compound,  or  to  make  them  up  iron  to  iron  with  no  compound?" 
In  this  connection,  several  bits  of  information  as  to  why  it  is 
desirable  to  use  some  compound  were  given.  Pipe  fittings  and 
the  threads  on  pipe  ends  are  not  always  uniform,  even  when 
coming  from  the  same  maker.  They  usually  rust  and  accumulate 
dirt  before  being  used,  so  that  they  go  together  hard;  threads  do 
not  fit  precisely,  and  fittings  may  leak,  particularly  under  high 
pressure;  also,  threads  not  served  with  compound  tend  to  cut 
when  screwed  together.  Moreover,  after  the  joint  is  made,  the 
threads  may  rust  together  and  make  it  difficult  to  unscrew  the 
pipe.  Red  lead  was  formerly  much  used  as  a  pipe  compound, 
to  lubricate,  preserve,  and  make  a  tight  joint,  but  nowadays  most 
steam  fitting  is  done  without  red  lead.  Graphite  and  oil,  mixed 
to  the  consistency  of  table  oil,  are  now  frequently  used,  and  are 
efficient  both  for  lubricating  and  making  a  tight  joint.  The 
compound  should  always  be  put  on  the  male  screw,  and  not 
daubed  into  the  female  end,  to  prevent  its  being  crowded  to  the 
rear  of  the  joint,  and  thus  reducing  the  clear  opening  of  the  pipe. 
It  is  necessary  to  keep  a  constant  watch  over  workmen  to  prevent 
them  from  putting  compound  into  the  female  end,  or  putting  it 
on  too  thick;  a  thin  coating  is  sufficient  to  get  the  desired  effect. 
Black  asphaltum,  about  as  thick  as  melted  butter,  is  also  used 
for  making  pipe  joints,  with  successful  results. 


251 


INDEX 


PAGE 

Accidents  to  motors  and  dyna- 
mos    240 

Air-lift   pump   as   elevator   for 

tailings  196 

Alloys  for  bearing  purposes ....  243 
Alloy,    kind    good    for    bearing 

purposes 243 

Alloys,  white  metal,  cheapest . .  243 

Ambrosovics,  Bela 239 

American  Hydraulic  Stone  Co .  .     32 
American  Smelting  and  Refining 

Co 31 

Anaconda  Copper  Mining  Co .  118, 120 
Antimony  and  lead  as  an  alloy.  243 

Angel,  H.  B 70 

Afgall,  Philip 84,  109,  164 

Ball-mill,  crushing  ability  of . . .   119 

Ferraris  type 132 

work  of 168 

Battery  foundations 75,  77 

ten-stamp,  horse-power  for    82 
Blaisdell  centrifugal  distributor, 

use  of 209 

excavator,  description  and 

use  of 206 

Hiram  W 204 

Blake  crushers,  capacity  of  ....     67 
Boilers,  internally  fired,  advan- 
tages of 240 

Boss,  Ira  C 75 

Boss,  M.  P 74,  77,  79,  156 

Brick,  hollow,  for  mill-building 

construction 28 

sand-lime  7 

Bricks,  development  of  industry  5,  7 

Brickwork   construction 24 

Broadbridge,  Mr 151 

Bronze,  plastic,  an  alloy 244 

Brown,  R.  Oilman 198 


Bullion-Beck  &  Champion  Min- 

ingCo 229 

Butters,  Charles. .  .203,  213,  224,  227 
Butters,  Charles  &  Co.,  Ltd. ...   203 

Cantilever  battery  frame 70 

Chilean  mill,  capacity  of. .  .119-121 

Mantey  offset  on 156 

principle  of 156 

product,  variations  in.  .122,  123 

Champion  Iron  Co 62 

Changing-house,   new,   at  Cliffs 

Shaft  mine 59 

Clamer,  G.  H 243 

Cleveland-Cliffs  Iron  Co 59 

Coal,  cost  of  drying 236 

drying,  notes  on 165 

-dust  firing 236 

pockets,  design,  of 58 

Collins,  George  E 130 

Concrete,  foundations  and  floors     18 
limestone  screenings  for  use 

in 10 

making  and  testing  of . . .  .14-17 

mixing  of 19 

mixture 8 

new  uses  of  in  building  con- 
struction       31 

requirements  for 9 

rubble 11 

systems 31 

work  about  mines 13 

Conveyors,  mechanical,  types  of 
(drag,  screw,  rotary,  re- 
ciprocating, etc.) ....  173-184 
Cost  of  plant  for  firing  coal-dust  236 

Coxe,  Eckley  B 178 

Crank,  Albert  F 203,  224,  227 

Crushing  costs,  details  of. .  .100,  101 
machinery,  modern 109 


253 


254 


INDEX 


Crushing  costs,  reduction  proper 

for  one  machine 110 

rolls,  springs  on 115 

Cyanide  vats,  handling  sand  for  203 

Discharge,  velocity  of,  how  to 

gage 221 

Dowling,  W.  R 149 

Dynamos  and  motors,  accidents 

to 240 

analysis  of  causes  of  acci- 
dents to 240 

Earthwork,  cost  of 3 

Edwards,  Henry  W 13 

Elevator,  belt 185 

belt,  details  of  operating  187- 

189 

bucket  belt,  for  tailings. . .   196 
for  tailings,  varieties ..  190,  198 

199 

El  Oro  Mining  and  Railway  Co.  212 
Evans-Chilean  mill 127 

Ferraris  ball-mill 132 

Fischer,  Hermann 137,  147 

Flint  mill,  operation  of 170 

Ford,  S.  A 250 

Gas,  transportation  of  by  pipe 

lines 249 

Gillette,  H.P 3 

Green,  Morris  M 176 

Griffin  mill,  output  of 167,  169 

Grinding  machinery,  modern. . .  109 

machines  used  at  Kalgoorlie  167 

Gromstetter,  Paul 70 

Griissner,  Mr 151 

Hardinge,  H.  W 154 

Harron,  Rickard  &  McCone. ...     74 

Howe,  Malverd  A 40 

Hunt,  Loren  E 39 

Huntington  mill  tests 125 

Ingalls,  W.  R.,5,  34,  45, 161, 173, 185 
Iron  buildings,  corrugated 33 


Iron,  corrugated,  prices  and  de- 
tails of 34-37 

Iron  and  steel  buildings 38 

Iron  and  steel,  protection  of . . .     51 

James,  Alfred 151 

Jennings,  Hennen 213 

Johnson,  J.  E.,  Jr 224 

Johnson,  J.  B 39 

Jones  &  Laughlin 37 

Kent,  William 36 

Ketchum,  Prof 38 

Kidder,  F.  E 33 

Krupp,    Fried.,    A.-G.    Gruson- 

werk   1.37 

Lanza,  Prof 40 

Laschinger,  E.  J 190,  198 

Lead  and  antimony  as  an  alloy.  243 

Lentz,  Herr 239 

Longdale  Iron  Co 232 

Lucius,  Albert 42 

Masonry,  brick 5 

McClintic  Marshall  Construction 

Co 42 

McCormack,  A.  C 240 

Metallic  Extraction  Co.  .  .84,  99,  104 

Mill  buildings,  design  of 23 

buildings,  lighting  of 26 

construction,  cost  of  brick- 
work       28 

cost  of  single-floor 24 

water,  economy  in 214 

Monier,  J 31 

Motors,    analysis    of    causes   of 

accidents  to 240 

and  dynamos,  accidents  to  240 
Mount  Morgan,  work  at. . .  .102-106 

New  Jersey  Zinc  Co 162 

North  American  Lead  Co 117 

Ore-bins,  design  of 58 

Ore,  dry  crushing  of 84 

drying 161 


INDEX 


255 


Ore,  drying,  apparatus  to  use,  161-163 

drying,  notes  on 165 

Osceola' Copper  Co 117 

Partitions,  dust-proof 64 

Pearce,  S.  H 149 

Peppel,  S.  V 5 

Peters,  Dr.  E.  D 227 

Pile-drivers,  capacity  of 235 

Pipe  joints,  making,  notes  on.  .  251 

line    construction 247 

line  in  the  United  States. .  247 

lines  for  natural  gas 247 

Power  plants,  small,  cost  of.  ...  245 

Raymond,  C.  A 26 

Regrinding  machinery 127,  130 

machines,  notes  on 118 

Robins,  Thomas,  Jr 182 

Robinson,  Mr 152 

Rolls  for  crushing,  proper  speed 

of 93 

for  crushing,  springs  on.  .  .  115 

efficiency  of 112 

Roof -construction,    saw-toothed  42 
Roofs  and  roof  coverings,  notes 

on    45 

tar  and  gravel 48-50 

Roskelly,  1 57 

Rothwell,  John  E 97 

Rubber,  adulterants  used  in.  .  .  233 

belting,  weight  of 235 

commercial,  apparently 
more  mineral  than  vege- 
table    234 

and  rubber  belting 233 

weight  of 233 

Sand,     handling     mechanically, 

cost  211 

handling    mechanically    for 

cyanide  vats 203 

-box,  section  of 220 

-box  in  water-saving  plant.  217 

piles,  efficiency  of 235 

removal  of  from  waste  water  224 

shoveler,  description  of . . .  225 


Sands,    plan    of    Virginia    City 

plant  for  treating 205 

Saw-toothed  roof  construction .  .     42 

Schwerin,  Martin 118,  127 

Scheffler,    Herr 239 

Scobey,  Jesse  C.,  214,  224,  225,  226, 

227 

Scott-Moncrieff,  G.  K 40 

Scraper,  details  of 218 

Searing,  Lewis 115 

Shepard,  Frank  E 82 

Slimes,  discharge  of 221 

Stamp  mill  construction 57 

tappets 79 

Stamps,  efficiency  of 112 

proper  use  of Ill 

Standard    Consolidated    Mining 

Co 198 

Stanford,  C.  P 70 

Steel  buildings 38 

protection  of 51,  54 

structural    work,    painting 

specifications  of 55 

Stephens-Toy  pulverizer 131 

Strong,  George  S 239 

Tailings,  disposal  of 201,  228 

elevators 190 

methods  of  clarifying 229 

pumps 195 

wheel 190-195 

Tank  at  Washington  Mills 225 

Tin,  use  of  in  alloys 244 

Timber,  notes  on 39 

Toch,  Maximilian 51 

Trent,  S.  V 127 

Trusses,  timber,  design  of 40 

Tube-mill,  movement  of  balls  in  146 

-mill  notes 151 

-mill,  operation  of,  how  ren- 
dered   visible 137 

-mill,  paths  of  motion  in. .    146 

-mill,  proper  size 153 

-mill,  table  of  diameters  and 

revolutions 148 

-mill,  theory  of  the 145 

-mills,  capacity  of 154 


256 


INDEX 


Vanderbilt,  Cornelius,  Jr 239 

Vezin,  H.  A 86 

VonMaltitz 70 

West,  H.  E 75,77 

Wheeler,  Zenos 70 

White,  H.  A 145 

White,  N.  F 84 

Water  supply,  method  for  saving  215 


PAGE 


Water-supply,    tanks,     wooden, 

proper  construction  of  . .  246 
Wilfley  tables,  operation  of. ...  214 

Wood,  W.  H 190,  198 

Workshops,  lighting  of 25 

Zimmerman,  C 25 

Zinc  white    an    adulterant    for 

rubber  . .  .  234 


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for 

City  Water  Works  Mineral  and  Hot  Water 

Irrigation  Systems  Out- Fall  Sewers 

Mining  and  Power  Plants        Steam  Pipe  Casing 

WE  MAKE  THE  BEST 

//'/  acid  proof  It  stands  the  pressure 

Illustrated  Catalog  Free 

NATIONAL  WOOD  PIPE  CO. 

SAN!FRANCISCO,  CAL.  Los  ANGELES,  CAL. 

OLYMPIA,  WASH.  SALT  LAKE  CITY,  UTAH 

Address  nearest  office 


Mining  and  Reduction  Machinery 


Double  Drum  Direct-Acting  Corliss  Hoists. 


Akron  Chilian  Mill. 


Crushing  Bolls. 

If  you  are  not  familiar  with  our 
line  of  Mining,  Reduction  and 
Power  Machinery,  etc.,  you 
should  write  for  our  printed 
matter  on  the  subject.  Write 
for  our  booklet,  "WHAT  WE 
DO,"  and  tell  us  which  of  the 
following  classes  of  equipment 
are  of  interest  to  you: 
Mine  Hoists  and  Equipment; 

(Steam  or  Electric) 
Milling  &  Crushing  Machinery; 
Smelting  Machinery; 

f  Water 
Power  Machinery  -s  Gas 

C  Steam 

Advise  us  of  any  equipment  re- 
quired or  contemplated  work  in 
our  line  and  we  will  gladly  pre- 
pare and  submit  bid  on  the 
work. 


Copper  Converter. 


New  York :  42  Broadway 

San  Francisco:  Atlas  Building 


GENERAL  OFFICES: 
CLEVELAND,  OHIO. 


BRANCH  OFFICES  : 

Chicago :  First  National  Bank  Building 
London,  Eng. :  47  Victoria  St.,  S.  W. 


"Pioneer" 
Rubber  Sanded  Roofing 

For  years  we  have  been  making  water-proof,  weather-proof, 
roofing  materials.  We  have  been  through  all  sorts  of  experi- 
ments and  tests.  We  have  been  learning  what  a  first-class 
roofing  should  be,  and  the  result  is  "Pioneer"  Rubber  Sanded 
Roofing. 

A  roofing  material  that  is  good  all  the  way  through,  every 
piece  that  goes  out  of  our  factory  is  backed  by  our  guarantee — 
we  make  it  from  start  to  finish  and  consequently  know  exactly 
what  goes  into  the  material  in  every  process.  We  know  that 
"Pioneer"  Rubber  Sanded  Roofing  will  back  up  every  claim 
we  make. 

In  addition  to  containing  all  the  good  qualities  of  the  best 
standard  roofings  on  the  market,  "Pioneer"  Rubber  Sanded 
Roofing  is  thoroughly  coated  with  a  wear-proof  surface  of  clean 
flint  sand. 

The  peculiar  climate  of  the  Pacific  Coast  is  more  severe  on 
roofs  and  roofing  materials,  than  any  other  climate  in  North 
America.  Tar  will  soften,  run,  and  clog  the  gutters  and  drain 
pipes  when  the  sun  is  hot,  and  will  crack  and  open  up  when  the 
air  gets  cool.  (We  wish  to  emphasize  the  fact  that  "Pioneer" 
Rubber  Sanded  Roofing  contains  absolutely  no  tar). 

Shingles  will  warp,  curl  and  split.  Tin  rusts  rapidly  and  soon 
becomes  leaky.  Corrugated  Iron  is  subject  to  excessive  expan- 
sion and  contraction,  opening  up  the  cracks  and  joints,  becoming 
useless  as  a  real  protection. 

"Pioneer"  Rubber  Sanded  Roofing,  overcomes  all  of  these 
difficulties,  furnishing  a  perfect  roof  covering,  with  a  big  saving 
in  the  cost.  What  we  claim  for  our  Rubber  Sanded,  is  this: — 
It  is  proof  against  everything  an  ideal  roofing  should  be  proof 
against. 

Manufactured  by 

PIONEER  ROLL  PAPER  CO. 
Los  Angeles,  Cal. 


. 


0753? 


184416 


